Rename index.md to _index.md and update crosslinks

Update terminology in api, editor_extensions, integrations and
operations docs

Update offering notes with all three offerings

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/172951#note_2234583979

Co-authored-by: Marcel Amirault <mamirault@gitlab.com>

As the name of this stage is changing, our docs metadata should
get updated as well.

This MR fixes a few small issues in the protected packages
documentation. It also adds the PATCH request type to the list of REST
API status codes, since we are using it for protected packages.

Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/457512

Changelog: fixed

These features can add changes that should be labelled accordingly.
They are exempt of ensure backward compatibility.

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/340419

Enables `keyset` pagination for `api/v4/projects/:id/repository/tree`
endpoint.

Changelog: added

Patch releases have been repurposed to include bug and security fixes,
deprecating the 'security release' terminology. This commit replaces the
'security release' term with 'patch release' throughout the codebase.

For details about this adjustment see https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/20113

Related to https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/20176

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

Remove use_registry_api_to_list_tags feature flag and
add notice re: availability of it in docs

Changelog: changed

Update format for admin and api docs