Merge branch 'mk-whats-new-docs' into 'master'

Create initial What's new documentation

See merge request gitlab-org/gitlab!58498

doc/administration/whats-new.md

+---
+stage: Growth
+group: Adoption
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
+---
+
+# What's new **(FREE)**
+
+With each monthly release, GitLab includes some of the highlights from the last 10
+GitLab versions in the **What's new** feature. To access it:
+
+1. In the top navigation bar, select the **{question}** icon.
+1. Select **What's new** from the menu.
+
+The **What's new** describes new features available in multiple
+[GitLab tiers](https://about.gitlab.com/pricing). While all users can see the
+feature list, the feature list is tailored to your subscription type:
+
+- Features only available to self-managed installations are not shown on GitLab.com.
+- Features only available on GitLab.com are not shown to self-managed installations.
+
+The **What's new** feature cannot be disabled, but
+[is planned](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/59011) for a future release.
+
+## Self-managed installations
+
+Due to our release post process, the content for **What's new** is not yet finalized
+when a new version (`.0` release) is cut. The updated **What's new** is included
+in the first patch release, such as `13.10.1`.