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

Otherwise the sync would crash, causing all later users not being synced.

Marked Geo as alpha

See merge request !2287

[ci skip]

[ci skip]

[ci skip]

Fix GitLab check: Problem with Elastic Search

Closes #2757

See merge request !2278

Empty repository mirror no longer creates master branch with README automatically

Closes #2425

See merge request !2276

Add License check for Burndown Charts

Closes #2578

See merge request !2219

Resolve "LDAP group link select dropdown error"

Closes #2762

See merge request !2277