New PR: Add content for enterprise-level overview dashboard (13512) (#50159)

Co-authored-by: Sam Browning <106113886+sabrowning1@users.noreply.github.com>
Co-authored-by: Felicity Chapman <felicitymay@github.com>

data/features/security-overview-dashboard-enterprise.yml

@@ -0,0 +1,5 @@
+# Reference: #11289
+# Documentation for the security overview dashboard, including for Enterprise-level
+versions:
+  ghec: '*'
+  ghes: '>3.13'

data/reusables/security-overview/beta-overview-dashboard.md

@@ -1,5 +1,9 @@
 {% note %}
 
+{% ifversion security-overview-dashboard-enterprise %}
+**Note:** The security overview dashboard is currently in beta and subject to change.
+{% else %}
 **Note:** The security overview dashboard is available at the organization level. The dashboard is currently in beta and subject to change.
+{% endif %}
 
 {% endnote %}

data/reusables/security-overview/filter-and-toggle.md

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+1. Use the options at the top of the overview page to filter the group of alerts you want to see metrics for. All of the data and metrics on the page will change as you adjust the filters.
+   - Use the date picker to set the time range that you want to view alert activity and metrics for.
+   - Click in the search box to add further filters on the alerts and metrics displayed.
+
+    ![Screenshot of the overview page in security overview. Filtering options are outlined in dark orange, including the date picker and search field.](/assets/images/help/security-overview/security-overview-dashboard-filters.png)
+
+1. For the alert trends graph at the top of the page, you can click **{% octicon "shield" aria-hidden="true"  %} Open alerts** or **{% octicon "shield-x" aria-hidden="true"  %} Closed alerts** to toggle between showing the trends for open or closed alerts. The toggle will only affect the alert trends graph. For more information, see "[Alert trends graph](#alert-trends-graph)."