- Explains how to use the Project Template
- Adds doc on how to migrate from GMA

We've decided to give the users the full power and responsibility of
managing their own Helmfiles. For this change, will use the
cluster-applications:v1.0.0+ which won't have the chart built-in anymore.

Those configurations related to the config.yaml file and all that logic
to allow the merge of values got removed from those Helmfiles. This
logic is not needed anymore since the files are no longer locked inside
the docker image and the user has full control of them over their
project template repository.

Also, it's worth noting that we're removing Ingress WAF which is
deprecated.

Another important point is that the Helmfiles being included here were
tested to work only against Helm3, which is expected from the
cluster-applications v1.0.0.

Some other work implemented here:

- Set all applications install default to true
   but the main Helmfile comments them out to not
   accidentally install/update anything.

- Use helm stable instead of gitlab stable archive.

- Use default branch instead of master for the CI.

- Default namespace to gitlab-managed-apps as a
   legacy to facilitate migration from GMA v1 and v2.

- Don't add a default insecure password to sentry DB.

- Remove missing file handlers
   Those are not needed anymore since we don't have logic
   over the existence of those helmfiles and the values
   files were all created by default even if blank.

- Update default runner image to ubuntu:20.04.

- Adds script to adopt CM CRDs and ClusterIssuer when the
user had previously installed CM through the UI.

- Vault chart is upgraded to 0.5.0 which is a necessary
   breaking change to comply with Helm v3.

Changelog: changed

Move utilities used for the Diffs app Tree Worker into a separate file

See merge request gitlab-org/gitlab!63449

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/63449

Fix unknown feature categorization

See merge request gitlab-org/gitlab!63368

Use Group Hierarchy Share Setting to Filter Search Results for Invite

See merge request gitlab-org/gitlab!63336

Update realtime assignee e2e spec waits

See merge request gitlab-org/gitlab!62487

Fix upload-file-experiment-trigger setting base route

See merge request gitlab-org/gitlab!63487

Update references to GitLab-managed apps with alternatives

See merge request gitlab-org/gitlab!63257

Merge branch '332139-vulnerability-counts-are-not-updated-when-a-scanner-filter-is-applied' into 'master'

Add Scanner ID filter to vulnerabilitySeveritiesCount

See merge request gitlab-org/gitlab!63335

Add tier badge to Code Review MR doc page

See merge request gitlab-org/gitlab!63556

Add tier badges to Source Code MR docs

See merge request gitlab-org/gitlab!63555

Add tier badge to Code Review-related MR doc page

Update the page titles with tier badges for Source Code-related MR docs

Document Content Editor component and Wiki integration

See merge request gitlab-org/gitlab!62580

Fix unintentional cleanup of Import/Export tmp files

See merge request gitlab-org/gitlab!63065

Get ancestors of an Epic using GraphQL

See merge request gitlab-org/gitlab!61154

Deprecate Attached Cluster Documentation

See merge request gitlab-org/gitlab!63102

Make project header section buttons responsive

See merge request gitlab-org/gitlab!62817

No behavior changes because setting cannot be changed yet

Document using distinct configuration for concurrent project sync

See merge request gitlab-org/gitlab!54538

Add caching around widget JSON [RUN ALL RSPEC] [RUN AS-IF-FOSS]

See merge request gitlab-org/gitlab!61584

Add UserCalloutDismisser component

See merge request gitlab-org/gitlab!63243

Replaces Klar by Trivy from the specs

See merge request gitlab-org/gitlab!62328

Remove PipelineUpdateWorker and PipelineProcessWorker build_ids Argument

See merge request gitlab-org/gitlab!63323

Update markup in merge_requests/_mr_title.html.haml

See merge request gitlab-org/gitlab!63187

Allow to insert highlighted code blocks in the Content Editor

See merge request gitlab-org/gitlab!63090

Made word list into headings

See merge request gitlab-org/gitlab!63478

Renamed all FFs from group::CI to Pipeline Execution [RUN ALL RSPEC] [RUN AS-IF-FOSS]

See merge request gitlab-org/gitlab!62968

Docs fix #214014

See merge request gitlab-org/gitlab!60672