Prior to this change a guest in a private group would end up in the
`groups_user_can_read_epics` branch of logic in
`#permissioned_related_groups`. This loops through each subgroup one at
a time checking permissions. Instead of unwinding that logic for now we
are just going to add a logical short circuit for a common specific
case.

The `#permissioned_related_groups` only needs to check if the user has
the ability to view all epics in all subgroups in a group. Previously we
were using the `read_confidential_epic` permission to confirm that the
user could access all epics in the subgroups as well. But this is not
necessary because this class will already filter confidential epics
later in `with_confidentiality_access_check` so really we just need to
answer the question "Can a user view all epics in this group and all of
it's subgroups". This seems deceptively like we could just check the
`read_epic` permission but there is a weird edge case for public groups.
A user can view epics in a public group even if they aren't a member but
that public group can contain private subgroups and they won't be able
to view those epics. So we can conclude that if a group is `private?` as
well as the user having the ability to `read_epic` in that group then
they will also be able to `read_epic` in all child groups as well.

This MR also introduces a new explicit test for `guest` permissions with
confidential issues. The reason being that we don't appear to have any
such tests about guest users already and it may give us more confidence
that confidentiality filtering is working correctly prior to
implementing this optimization.

Update changelog to match final change

See merge request gitlab-org/gitlab!59334

Moved reference content to reference topic

See merge request gitlab-org/gitlab!59184

Add URL param for linking to a specific stage in group-level VSA

See merge request gitlab-org/gitlab!57621

Fix Rails/SaveBang offenses in spec/factories_spec.rb

See merge request gitlab-org/gitlab!58102

Compress documentation images

See merge request gitlab-org/gitlab!59280

Recommend to fill gaps in enum values

See merge request gitlab-org/gitlab!58759

Update codequality documentation

See merge request gitlab-org/gitlab!59166

Reduce pipeline tooltip delay to 0

See merge request gitlab-org/gitlab!59155

Change language on welcome page

See merge request gitlab-org/gitlab!59183

Externalize strings in projects/index.html.haml

See merge request gitlab-org/gitlab!58160

Rename find to execute in EnvironmentsFinder

See merge request gitlab-org/gitlab!59254

Include user permission export screenshot

See merge request gitlab-org/gitlab!59301

Merge branch '325778-moving-issue-to-board-list-of-different-type-should-not-remove-it-from-previous-list' into 'master'

Clone issue card on move when necessary [RUN AS-IF-FOSS]

See merge request gitlab-org/gitlab!58644

Fix FOSS specs broken by !58833 [RUN ALL RSPEC] [RUN AS-IF-FOSS]

See merge request gitlab-org/gitlab!59306

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/58833 was merged,
but broke some FOSS specs because the code was moved to `ee/` while
the corresponding specs were not moved.

Remove issue_perform_after_creation_tasks_async feature flag [RUN ALL RSPEC] [RUN AS-IF-FOSS]

See merge request gitlab-org/gitlab!59042

Removes compliance framework administration abilities from subgroups

See merge request gitlab-org/gitlab!58873

Add OncallScheduleEntity to users in Admin helper

See merge request gitlab-org/gitlab!59093

Align UI to use "Runtime" for CI/CD job page

See merge request gitlab-org/gitlab!58838

Updates the text on the jobs page so that we use clear
language to talk about the time it takes a job to run.

Create a migration to insert trail plans

See merge request gitlab-org/gitlab!57814

Refactor to using Vuex modules for project/group members views

See merge request gitlab-org/gitlab!58828

Add cop Style/RegexpLiteralMixedPreserve [RUN AS-IF-FOSS]

See merge request gitlab-org/gitlab!58898

Fix dropdown toggle bug

See merge request gitlab-org/gitlab!59309

Fix Rails/SaveBang Rubocop offenses for email handlers

See merge request gitlab-org/gitlab!58095

Externalize strings in shared/_sign_in_link.html.haml

See merge request gitlab-org/gitlab!58283

Resolve "Update screenshots for menu and sidebar UI updates - Manage"

See merge request gitlab-org/gitlab!58511