[March 15] Dependabot version updates support for private registries (#17985)

* Update the UI for allowing private repos

* Private reg support WiP

* More WiP for private reg support

* Apply review comment about internal repos

* Add Dependabot secrets article

plus details of allowing remote code execution

* Add link to private registries info

* Fix conflict on PR

* Add 'private_source_*' errors to troubleshooting

* Update content/github/administering-a-repository/configuration-options-for-dependency-updates.md

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>

* Update content/github/administering-a-repository/managing-encrypted-secrets-for-dependabot.md

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>

* Update content/github/administering-a-repository/managing-encrypted-secrets-for-dependabot.md

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>

* Update content/github/administering-a-repository/managing-encrypted-secrets-for-dependabot.md

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>

* Update content/github/administering-a-repository/managing-encrypted-secrets-for-dependabot.md

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>

* Update content/github/setting-up-and-managing-organizations-and-teams/managing-security-and-analysis-settings-for-your-organization.md

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>

* Update data/reusables/dependabot/private-dependencies-note.md

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>

* Update data/reusables/dependabot/supported-package-managers.md

Co-authored-by: Mike McDonald <2575327+asciimike@users.noreply.github.com>

* Update content/github/administering-a-repository/configuration-options-for-dependency-updates.md

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>

* Update content/github/administering-a-repository/configuration-options-for-dependency-updates.md

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>

* Update content/github/administering-a-repository/configuration-options-for-dependency-updates.md

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>

* Update content/github/administering-a-repository/configuration-options-for-dependency-updates.md

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>

* Update content/github/administering-a-repository/configuration-options-for-dependency-updates.md

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>

* Update content/github/administering-a-repository/configuration-options-for-dependency-updates.md

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>

* Update content/github/administering-a-repository/configuration-options-for-dependency-updates.md

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>

* Update content/github/administering-a-repository/configuration-options-for-dependency-updates.md

Co-authored-by: Mike McDonald <2575327+asciimike@users.noreply.github.com>

* Update content/github/administering-a-repository/configuration-options-for-dependency-updates.md

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>

* Update content/github/administering-a-repository/managing-encrypted-secrets-for-dependabot.md

Co-authored-by: Jason Rudolph <jason@jasonrudolph.com>

* Update content/github/administering-a-repository/configuration-options-for-dependency-updates.md

Co-authored-by: Mike McDonald <2575327+asciimike@users.noreply.github.com>

* Update content/github/administering-a-repository/configuration-options-for-dependency-updates.md

Co-authored-by: Mike McDonald <2575327+asciimike@users.noreply.github.com>

* Move registries section below updates

as requested by reviewer.

* Correct heading level of 'allow' subheading

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>
Co-authored-by: Mike McDonald <2575327+asciimike@users.noreply.github.com>
Co-authored-by: Jason Rudolph <jason@jasonrudolph.com>

content/github/managing-security-vulnerabilities/troubleshooting-dependabot-errors.md

@@ -76,9 +76,20 @@ There are separate limits for security and version update pull requests, so that
 
 The best way to resolve this error is to merge or close some of the existing pull requests and trigger a new pull request manually. For more information, see "[Triggering a {% data variables.product.prodname_dependabot %} pull request manually](#triggering-a-dependabot-pull-request-manually)."
 
-#### {% data variables.product.prodname_dependabot %} can't resolve your dependency files
+#### {% data variables.product.prodname_dependabot %} can't resolve or access your dependencies
 
-If {% data variables.product.prodname_dependabot %} attempts to check whether dependency references need to be updated in a repository, but can't access one or more of the referenced files, the operation will fail with the error message "{% data variables.product.prodname_dependabot %} can't resolve your LANGUAGE dependency files." The API error type is `git_dependencies_not_reachable`.  
+If {% data variables.product.prodname_dependabot %} attempts to check whether dependency references need to be updated in a repository, but can't access one or more of the referenced files, the operation will fail with the error message "{% data variables.product.prodname_dependabot %} can't resolve your LANGUAGE dependency files." The API error type is `git_dependencies_not_reachable`.
+
+Similarly, if {% data variables.product.prodname_dependabot %} can't access a private package registry in which a dependency is located, one of the following errors is generated:
+
+*	"Dependabot can't reach a dependency in a private package registry"<br>
+   (API error type: `private_source_not_reachable`)
+*	"Dependabot can't authenticate to a private package registry"<br>
+   (API error type:`private_source_authentication_failure`)
+*	"Dependabot timed out while waiting for a private package registry"<br>
+   (API error type:`private_source_timed_out`)
+*	"Dependabot couldn't validate the certificate for a private package registry"<br>
+   (API error type:`private_source_certificate_failure`)
 
 To allow {% data variables.product.prodname_dependabot %} to update the dependency references successfully, make sure that all of the referenced dependencies are hosted at accessible locations.