Also fixes links to section headings that
have changed.

Also make security warning more visible and
improves instructions.

Many code blocks are 4spaced, and they render in GitLab
without coloring as a result, even though they are
fenced with a language label. If in a list, other items
woll render as being in a code block too, even if not
meant to. This fixes all these issues, and cleans up
minor whitespace issues in /user, /security, /ssh
and /migrate_ci_to_ce docs.

Remove unneeded trailing whitespace in lines in
/security /workflow /user docs

GitLab uses a kubernetes service account to perform deployments. For
serverless deployments to work as expected with externally created
clusters with their own knative installations (e.g. via Cloud Run), this
account requires additional permissions in the serving.knative.dev API
group.

Add relevant webcast to drive traffic and MQLs

See merge request gitlab-org/gitlab-ce!30236

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