[ci skip]

Deprecated GitLab CI API clean up

Deprecated GitLab CI API clean up.

The intent here is to clean up deprecated GitLab CI documentation leaving only relevant information.
Since we merged `Ci::Project` to `Project` most of this documentation is outdated.

Closes #13610 

See merge request !3003

add bundle clean to upgrade docs

This MR adds a bundle clean after installing new gems. Bundle clean removes old, not needed gems to keep the system clean.

See merge request !2809

Added Troubleshooting information for most used services.

This replaces the changes started at gitlab-com/www-gitlab-com!1603

I'd like to add similar troubleshooting information for EE only services, but that needs to happen on a different MR on the EE side. Probably after this one gets merged.

cc @ernstvn @dblessing @balameb @cabargas @kelvinmutuma 

See merge request !3080

Document changes to the initial admin password

Addresses https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3068#note_4117550

[ci skip]

See merge request !3120

[ci skip]

Remove redundant integration tests

These three tests were essentially checking that adding a note to
something updated its `noteable`'s `updated_at` attribute.

This is well-tested Rails behavior and we shouldn't feel the need to
write an integration test to verify it. At most we should be ensuring
that the association definition adds the `touch: true` option, which we
now do in Note's unit test.

See merge request !3117

Set cache headers for raw blobs

This changes allows browsers and (in the case of public projects)
proxy caches to cache raw Git blob responses.

See merge request !3113

[ci skip]

These three tests were essentially checking that adding a note to
something updated its `noteable`'s `updated_at` attribute.

This is well-tested Rails behavior and we shouldn't feel the need to
write an integration test to verify it. At most we should be ensuring
that the association definition adds the `touch: true` option, which we
now do in Note's unit test.