Makes use of markdownlint for automated cleanup

Because for now, we're changing the format.

Related to: https://gitlab.com/gitlab-org/gitlab-docs/-/issues/1751

Try to use standard language for linking to the yaml
reference, but also fix links to the correct locations

Update the links in all docs except user and admin pages

This is not used on the current docs website
and needs to be removed for future compatibility
with Hugo.

Also updating links to Service Desk docs in-product.

Changelog: fixed

Split long lines, remove extra whitespace, change CI to
CI/CD as needed, and similar non-content changing tweaks

Adds documentation detailing how to perform a migration
from GitHub Actions to GitLab CI. This documentation will
describe key similarities and differences, compare syntax,
and define deployment steps.

Performs an Overhaul of the current Jenkins
Migration documentation to include detailed
examples of key differences, syntax, migration
steps, and more.

Updating screenshots in example

Also rename file to use underscores and not hyphens

Also compresses the images

Simplify language as much as possible, lower the visibility
of some details, remove deprecated details. Also, focuses more
on GitLab CI/CD than Jenkins itself.

We can simplify the CI docs significantly by relying on
improved navigation bar structure and improved search

Because we changed the way we
do the markdown.

Related to: https://gitlab.com/gitlab-org/gitlab-docs/-/issues/1690

Related to: https://gitlab.com/gitlab-org/gitlab/-/issues/384335

- /doc/policy/experiment-beta-ga-support.md
- /doc/policy/alpha-beta-support.md

Split job artifacts page into a main topic page
and a separate troubleshooting page. Also, move both
to be nested under ci/jobs rather than ci/pipelines

The disqus integration was removed from the docs site,
so these identifiers don't do anything now.

List security related features together, move
crosslinks into related topics section, remove
information that is repeated in other places.

The page can be simplified with better layout
and section naming. Some sections can be completely
removed for easier scanning.