Backport doc/user/group/img/groups.png changes from EE

See merge request gitlab-org/gitlab-ce!21415

Add changelog entries for 11.2.3 and 11.1.6

See merge request gitlab-org/gitlab-ce!21425

Allow whitelisting for "external collaborator by default" setting

See merge request gitlab-org/gitlab-ce!17711

Fixed project logo when it is LFS tracked

Closes #47229

See merge request gitlab-org/gitlab-ce!20948

Resolve "Users stuck on a redirect loop after transferring project"

Closes #41292

See merge request gitlab-org/gitlab-ce!21408

Resolve "Make a Rubocop cop to prefer class_methods over ClassMethods for ActiveSupport::Concern"

Closes #50414

See merge request gitlab-org/gitlab-ce!21379

Updates hint text for merging branches locally.

Closes #39398

See merge request gitlab-org/gitlab-ce!21421

Fix Error 500s due to encoding issues when Wiki hooks fire

Closes #50590

See merge request gitlab-org/gitlab-ce!21414

- Hint essentially states that a user should first update their target branch
  with upstream changes and then perform the merge.

Fix Emojis cutting in the right way

Closes #47913

See merge request gitlab-org/gitlab-ce!21413

These changes were introduced in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6622
but should have originated in CE.

Saved Wiki content goes through the GitalyClient::WikiService, which calls
StringIO#set_encoding on the input stream. The problem is that this call
mutates the encoding of the given string object to ASCII-88BIT, which
causes problems for models expecting the data to still be in UTF-8.

Freezing the input disables this behavior:
https://github.com/ruby/ruby/blob/v2_4_4/ext/stringio/stringio.c#L1583

Closes #50590

Move package-and-qa to the test phase

Closes #50718

See merge request gitlab-org/gitlab-ce!21400

Resolve "Consider reorganizing the QA scenarios"

Closes #49800

See merge request gitlab-org/gitlab-ce!20931

Fix #47913 (again), revert !21180, fix regression of !8652, improve !20137

Resolve "Error getting performance bar results for <UUID>"

Closes #50801

See merge request gitlab-org/gitlab-ce!21411

This isn't interesting most of the time and is may go over other flash banners.

These don't have performance data saved as they use Grape.

Rails 5: replace removed silence_stream

See merge request gitlab-org/gitlab-ce!21387

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Previously, this wasn't needed: text was normally set to the highlighted
contents anyway. Now, it is: we store different things in text and rich_text.

This caused https://gitlab.com/gitlab-com/production/issues/439.

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