+ clean transaction metrics

+ Gemfile.lock file update

+ Cleanup sampler, use latest Prometheus gem

Resolve "Add a `merge_request_diff_id` column to `merge_requests`"

See merge request gitlab-org/gitlab-ce!15035

Refactor responsive table styles to support nested error block

See merge request gitlab-org/gitlab-ce!15145

Incorporate Gitaly's OperationService.UserFFBranch RPC

Closes gitaly#693

See merge request gitlab-org/gitlab-ce!15040

Once we migrate existing MRs to have this column, we will be able to get the
latest diff for a single merge request more efficiently, and (more importantly)
get all latest diffs for a collection of MRs efficiently.

We already had this the other way around (merge_request_diffs.merge_request_id),
but this is needed to gather only the most recent diffs for a set of merge
requests.

Update .nvmrc to v9.0.0 (current stable)

See merge request gitlab-org/gitlab-ce!15149

Convert Icons in CI to SVG Sprite Icons

See merge request gitlab-org/gitlab-ce!14567

Document GitLab pages prerequisite with external HTML artifacts

See merge request gitlab-org/gitlab-ce!15153

Send SIGSTP before SIGTERM to actually give Sidekiq jobs 30s to finish when the memory killer kicks in

See merge request gitlab-org/gitlab-ce!15102

Remove Private Tokens

Closes #38595 and #38447

See merge request gitlab-org/gitlab-ce!14838

Remove an exception from the git user default SSH config check

See merge request gitlab-org/gitlab-ce!15151