Related Issues UI Polish

Closes #2756

See merge request !2268

Default `authorized_keys_enabled` setting to true

Closes #2738

See merge request !2240

Remove prop because it no longer contains "related issue" in it
and probably doesn't need to be customized anymore

See https://gitlab.com/gitlab-org/gitlab-ce/issues/34336

See https://gitlab.com/gitlab-org/gitlab-ce/issues/34336

See https://gitlab.com/gitlab-org/gitlab-ce/issues/34336

See https://gitlab.com/gitlab-org/gitlab-ce/issues/34336

See https://gitlab.com/gitlab-org/gitlab-ce/issues/34336

See https://gitlab.com/gitlab-org/gitlab-ce/issues/34336

Geo - Fix log message when trying to sync a project with invalid id

Closes #2784

See merge request !2294

Clarify the expiration date of PATs

See merge request !2198

Do the work synchronously to avoid multiple workers attempting to add batches of keys at the same time.

Also, make the delete portion wait until after adding is done.

Reminder: The original migration was fixed retroactively a few commits ago, so people who did not ever run GitLab 9.3.0 already have a column that defaults to true and disallows nulls. I have tested on PostgreSQL and MySQL that it is safe to run this migration regardless.

Affected customers who did run 9.3.0 are the ones who need this migration to fix the authorized_keys_enabled column.

The reason for the retroactive fix plus this migration is that it allows us to run a migration in between to fix the authorized_keys file only for those who ran 9.3.0.

Locally, if Spring was not restarted, `current_application_settings` was still cached, which prevented the migration from editing the file. This will also ensure that any app server somehow hitting old cache data will properly default this setting regardless.

This allows us to identify customers who ran the broken migration. Their `authorized_keys_enabled` column does not have a default at this point.

We will fix the column after we fix the `authorized_keys` file.

This reverts commit fce9c01b, reversing
changes made to b1003408.

To reiterate: this reverts a revert.

Resolve "Unable to rebase unapproved merge request"

Closes #2753

See merge request !2273

Detect Geo secondary role properly in spec/support/db_cleaner.rb

See merge request !2282

Return `nil` when user is not found by email.

Closes #2769

See merge request !2289

Add CE-to-EE guide for 9.3

See merge request !2254

Perform Geo::RepositorySyncService for dirty projects

See merge request !2130

Geo - Fix path_with_namespace for instances of Geo::DeletedProject

Closes #2726

See merge request !2267

Move shared examples to their correct location and remove duplicates

Closes #2759

See merge request !2281

Introduce unified docs to EE landing page

See merge request !2265