Removes milestone from cluster base domain documentation

See merge request gitlab-org/gitlab-ce!25045

(cherry picked from commit 84c9b1e7)

13a64a5c Removes milestone from cluster base domain

Uses the preferred way for introduced blocks instead of notes, on
auto devops and cluster documentation.

Also fixes some typos.

The changes are included for project and group cluster documentation
pages. Also specifies that AUTO_DEVOPS_DOMAIN will be deprecated on 12.0

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/52363

- Also makes other minor Markdown fixes that were near the main fixes.

Cross link from GitLab CI variable doc too

Add note about running pods and updating secrets without any code change

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/45279

This reverts merge request !23165

Let users know we do two Helm releases if they specify DB_INITIALIZE.

Auto DevOps deployment strategies now supports timed incremental
rollout. We are deprecating the usage of INCREMENTAL_ROLLOUT_ENABLED
environment variable in Auto DevOps template.

The new behavior will be driven by the INCREMENTAL_ROLLOUT_MODE variable
that can either be manual (same as INCREMENTAL_ROLLOUT_ENABLED) or
timed.

Rollout deployments will be executed using a 5 minute delay between each
job.

* Limitation of DB_INITIALIZE (run once)
* helm hooks
* Examples

Originally submitted at
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6724

.

Signed-off-by: Rémy Coutable <remy@rymai.me>

Minor typo fix CODE_QUALITY seems to have a `_` in it in .gitlab-ci.yml default templates, and to wit, without `_` seems to have no effect