Write docs on how to take over any previously installed GMA v1 applications

We need to have docs to tell users how to:

1. Check if they have any previously installed GMA v1 applications
2. How to uninstall GMA v1 application if they wish to
3. Nice to have: how to maintain / upgrade the GMA v1 application

Release notes

1-click GitLab Managed Applications are being removed from GitLab in version 14.0. Today, we publish a set of documentation that describes how users of GitLab Managed Applications can continue using these applications and how can they take ownership of them.