Update OpenAPI Description (#56428)

Co-authored-by: Sam Browning <106113886+sabrowning1@users.noreply.github.com>
Co-authored-by: Hirsch Singhal <1666363+hpsin@users.noreply.github.com>

content/rest/enterprise-admin/index.md

@@ -27,6 +27,7 @@ children:
   - /management-console
   - /network-configurations
   - /org-pre-receive-hooks
+  - /organization-installations
   - /orgs
   - /pre-receive-environments
   - /pre-receive-hooks

content/rest/enterprise-admin/organization-installations.md

@@ -0,0 +1,13 @@
+---
+title: REST API for managing organization GitHub App installations
+shortTitle: GitHub App installations
+intro: Use the REST API to manage which {% data variables.product.prodname_github_apps %} are installed in your enterprise's organizations.
+versions: # DO NOT MANUALLY EDIT. CHANGES WILL BE OVERWRITTEN BY A 🤖
+  ghec: '*'
+topics:
+  - API
+autogenerated: rest
+allowTitleToDifferFromFilename: true
+---
+
+<!-- Content after this section is automatically generated -->