Only render fixed number of mermaid blocks

See merge request gitlab/gitlabhq!3411

Merge branch 'security-12717-fix-confidential-issue-assignee-visible-to-guests-12-3' into '12-3-stable'

Display only participants that user has permission to see

See merge request gitlab/gitlabhq!3421

Redirect user to root path after unsubscribing from private resource

See merge request gitlab/gitlabhq!3423

Hide disabled project milestones in project settings on group level

See merge request gitlab/gitlabhq!3424

Add policy check if cross reference system notes are accessible

See merge request gitlab/gitlabhq!3426

Cancel all running CI jobs when user is blocked

See merge request gitlab/gitlabhq!3436

Filter not accessible label events

See merge request gitlab/gitlabhq!3440

Label events may use cross-project or cross-group references,
if the projects are not accessible by user, we don't show these
label events.

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This prevents a MITM attack where attacker could
still access Git repository if any jobs were
running long enough.

If user unsubsrcribes from a resource that they no longer have
access to they should not be revealed the resource path, but be
redirected to app root instead.

https://gitlab.com/gitlab-org/gitlab-ce/issues/64938

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