Follow-up to 34560a16 & 89c34dfb

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

Artifacts goes to PE, Variables to PA

This paragraph should have been removed in
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/155757.

There has been much confusion about how CI job artifacts downloads
work with the runner, so this commit attempts to clarify how
all the parts work together.

Because for now, we're changing the format.

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

Co-authored-by: Keelan Lang <klang@gitlab.com>

Update the links in all user and admin pages

Related to: https://gitlab.com/gitlab-org/technical-writing/-/issues/838

Also moved images in continuous integration file

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

- Move paragraphs around so that make more sense and be more fluid.
- Rename "Consolidated object storage configuration" section to
  "Configure a single storage connection for all object types"
- Rename "Common parameters" section to "Configure the common
  parameters"
- Rename "Object-specific configuration" to "Configure the parameters of
  each object". This was bugging me for a while. We also have
  "Storage-specific configuration" which is about configuring each
  object type separately with different credentials. I almost always
  never knew which one referred to what.
- Rename "Storage-specific configuration" to "Configure each object type
  to define its own storage connection"

Reorder sections, nesting subsections under the
related parent sections and simplify headers. Also,
remove screenshots that aren't needed, and simplify the
download artifacts section, and fix UI text that was
incorrect, adding SVGs instead of screenshots.

Pipeline Insights becomes Pipeline Security, and
many categories shifted around.

Some users use a Windows share via CIFS to hold their job
artifacts. CIFS file leasing may cause "invalid argument" errors for
job artifacts. Document ways to work around this issue.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/389995

There are many words flagged as failing the spelling rule
which have underscores. It's likely these are code references
that need backticks, or need the underscore removed.

Since https://gitlab.com/gitlab-org/gitlab/-/merge_requests/97170 it
is impossible to enable background_upload. This commit removes
documentation that talks about cases where background_upload is
enabled.

Changelog: other

This removes a step from the documented process for migrating objects
from object storage to local storage in the cases of CI artifacts, LFS
objects and uploads. This step is both no longer necessary and broken:
if the user carries out the step they get an error in Omnibus.

See https://gitlab.com/gitlab-com/gl-infra/scalability/-/issues/1931.

Changelog: fixed

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