Signed-off-by: Nailia Iskhakova <niskhakova@gitlab.com>

Bump PG default version in preparation for PG17

Changelog: changed

* My primary motivation here was to move the contents of the new-ish
  "References" section into a comment
* I also moved the MR acceptance checklist to the bottom beacuse that
  is always the same, so it's the least important context to get when
  looking at an MR.

Remove unnecessary inherits

Remove .gitlab-qa-install extends

Remove qa-base reference

Update notify-slack job

Update the way variables are triggered

Set ruby version in pipeline creator

Extract omnibus e2e test base job

Extract common e2e test variables

Inherit omnibus cache related variables

Move definition to omnibus

Skip clone for release-set job

Use OS variables for omnibus qa job images

- /scripts/generate-failed-test-on-omnibus-mr-message.rb
- /scripts/generate-message-to-run-e2e-pipeline.rb
- /doc/development/testing_guide/end_to_end/beginners_guide/page_objects.md
- /doc/development/testing_guide/end_to_end/beginners_guide/resources.md
- /doc/development/testing_guide/end_to_end/_index.md
- /doc/development/ai_features/duo_chat.md
- /spec/scripts/generate_message_to_run_e2e_pipeline_spec.rb
- /.gitlab/issue_templates/Feature Flag Roll Out.md
- /danger/stable_branch_patch/Dangerfile
- /qa/qa/scenario/test/sanity/selectors.rb

To be run in backport MRs
to test upgrade from patch and to patch
before it's released

Signed-off-by: Nailia Iskhakova <niskhakova@gitlab.com>

In preparation for adding support for PG 17, these tests
ensures the basic level of compatibility for Postgres

Note: PG17 integration jobs for opensearch and es8 were
disabled for now, as they'll exceed the limits of jobs
that a pipeline can have

Changelog: changed

Files that can affect docs builds should be listed
as requiring optional TW approval, to include TW team
when needed

Changelog: changed

As PG16 is the production DB, is important
to have all related specs running.

Changelog: changed

This reverts merge request !172742

There are many RuboCop cops used internally, which have inline
documentation.

These cops can now have documentation generated for them automatically,
so GitLab developers and contributors can reference our documentation
and examples, to better understand the cops as well as the reasoning
behind our decisions.

Also make sure to run rubocop-docs and eslint-docs
jobs when the underlying tooling is updated

Changelog: performance

This fixes that the `ui-docs-links lint` references the old
`DocumentationLinks` linter that was removed in [1].

[1]: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/181453

Also updates links to gitlab-docs project