Also fixes instances in Markdown that broke the rule.

Previously, we used brackets to denote the tier badges,
but this made Kramdown, the docs site Markdown renderer,
show many warnings when building the site. This is now
fixed by using parentheses instead of square brackets.

This was caused by [PREMIUM] looking like a link to
Kramdown, which couldn't find a URL there.

See:
- https://gitlab.com/gitlab-com/gitlab-docs/merge_requests/484
- https://gitlab.com/gitlab-org/gitlab-ce/issues/63800

First MR in a series updating all redirected links
in CE documentation to the destination URLs

Fixing square brackets, links, etc in:
  merge_requests.md
  vulnerabilities.md
  issues.md
  issues_statistics.md
  pipelines.md
  services.md
  group_milestones.md
  milestones.md
  runners.md
  changelog.md
  issue_workflow.md
  elasticsearch.md
  api_graphql_styleguide.md
  automatic_ce_ee_merge.md
  file_storage.md
  architecture.md
  database_debugging.md
  index.md
  index.md
  frontend_testing.md
  pry_debugging.md
  vue.md
  development_process.md

Allow asynchronous rebase operations to be monitored

Closes #54117

See merge request gitlab-org/gitlab-ce!29940

Many small fixes to api docs which were merged from EE to CE,
and tables cleaned up, as noted in issue
https://gitlab.com/gitlab-org/gitlab-ce/issues/64072

This MR introduces tracking of the `rebase_jid` for merge requests. As
with `merge_ongoing?`, `rebase_in_progress?` will now return true if a
rebase is proceeding in sidekiq.

After one release, we should remove the Gitaly-based lookup of rebases.
It is much better to track this kind of thing via the database.