We do not need to link to index files, and in the future
it will be recommended to avoid it.

Also rename index files for user/namespace, user/operations_dashboard,
and user/organization, and update crosslinks.

Also update crosslinks from docs and UI

Changelog: changed

Also updates all crosslinks including from UI code

Changelog: changed

H1 headers needs to be in YAML frontmatter now

Rename index.md to _index.md and update links
across all files.

Changelog: changed

Updates all version history to use GitLab Self-Managed,
as the correct name for the self-managed offering

Because we have a new standard

Update offering notes with all three offerings

Give these images milestone numbers so we can tell how old they are.

Co-authored-by: Lysanne Pinto <lpinto@gitlab.com>

Co-authored-by: Phillip Wells <pwells@gitlab.com>

Related to: https://gitlab.com/gitlab-org/gitlab/-/issues/439130

Update the links in all user and admin pages

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

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.

Because we changed the way we
do the markdown.

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

Follows:
https://docs.gitlab.com/ee/development/documentation/versions.html#deprecate-a-page-or-topic

Related epic: https://gitlab.com/groups/gitlab-com/-/epics/1940

Adds links to the issue which changes the feature flag.

Adds notes abouthow to toggle the feature flag.

Remove tiers from version history

Related to: https://gitlab.com/gitlab-org/technical-writing/-/issues/528
We want to standardize on lowercase
See the recommended word list for details

We standardized on this usage. See the Word List for
details: https://docs.gitlab.com/ee/development/documentation/styleguide/word_list.html