Avoid plucking Todo ids in TodoService - take 2

See merge request !11415

Use mixin for new dropdown style

See merge request !13274

implement #inspect for all Referables

See merge request !13285

fix #3686 make tarball download url to end with extension

Closes #3686

See merge request !13178

Don't include EmailHelpers manually, pick with rspec

See merge request !13257

fix #35133 strip new lines from ssh keys

Closes #35133

See merge request !13234

Re-organise "issues" indexes for faster ordering

See merge request !13278

Fixed sign-in restrictions buttons not toggling active state

Closes #35882

See merge request !13270

Migrate Gitlab::Git::Repository#count_commits to Gitaly

Closes gitaly#415

See merge request !13121

Merge request commits background migration

See merge request !12685

When trying to run an UPDATE, this query is ran:

```sql
UPDATE `todos`
INNER JOIN `projects` ON `projects`.`id` = `todos`.`project_id`
SET `todos`.`state` = 'done'
WHERE `todos`.`user_id` = 4
  AND (`todos`.`state` IN ('pending'))
  AND (EXISTS
         (SELECT 1
          FROM `project_authorizations`
          WHERE `project_authorizations`.`user_id` = 4
            AND (project_authorizations.project_id = projects.id))
       OR projects.visibility_level IN (10,
                                        20))
  AND `projects`.`id` IN
    (SELECT `todos`.`project_id`
     FROM `todos`
     WHERE `todos`.`user_id` = 4
       AND (`todos`.`state` IN ('pending')))
  AND (`todos`.`state` != 'done')
```

But MySQL does not like the subquery used to filter on
`projects.id IN (SELECT ...`

Because the subquery queries from the same table:

> Error: You can’t specify target table ‘todos’ for update in FROM clause

So as workaround, wrap it in another subquery, where the original
subquery is aliased using the `AS` statement.

Mostly inspired by https://stackoverflow.com/a/43610081/89376

TodoService should not call `.select(&:id)` on todos, because this is
bad performance. So instead use sub-queries, which will result in a
single SQL query to the database.

https://docs.gitlab.com/ee/development/sql.html#plucking-ids

Move API "basic usage" to be more visible

See merge request !13171

Update reply_by_email_postfix_setup.md, included starting courier-authdaemon after installation.

See merge request !13218

`:mailer` is needed to pick it easily, while
`type: :mailer` is needed for picking it automatically for
tests located in spec/mailers/*_spec.rb

It's a bit complicated in spec/services/notification_service_spec.rb
but we'll leave it alone for now.

fix Jump to next discussion

Closes #35232

See merge request !13076

By adding various composite indexes we can reduce the time spent
retrieving issue lists. Because of the way these indexes are built
column wise we can also remove some standalone indexes, keeping the
total number of indexes in check.

Make dropdown style on project page consistent

Closes #35778

See merge request !13193

Don't send rejection mails for all auto-generated mails

Closes #28472

See merge request !13254

Previously, we stored these as serialised fields - `st_{commits,diffs}` - on the
`merge_request_diffs` table. These now have their own tables -
`merge_request_diff_{commits,diffs}` - with a column for each attribute of the
serialised data.

Add a background migration to go through the existing MR diffs and migrate them
to the new format. Ignore any contents that cannot be displayed. Assuming that
we have 5 million rows to migrate, and each batch of 2,500 rows can be
completed in 5 minutes, this will take about 7 days to migrate everything.

Ensure we run installation Rake tasks in a clean env in TestEnv

Closes #35859

See merge request !13249

This would be much more accurate. We assume this is an
auto-generated email if such header is provided, and
the value is not "no". It could also be: "auto-generated",
"auto-replied", or other values from extension. It seems
that only "no" could mean that this is sent by a human.

See: https://tools.ietf.org/html/rfc3834

Closes #35882

Do not validate CSRF token in API unless needed

Closes #35705

See merge request !13256

Remove test gitaly when older than version file

See merge request !13250

Fly-out dropdown menu in new sidebar

Closes #34026

See merge request !12938

Fix Prometheus application settings help link to point to Prometheus help page

Closes #33921

See merge request !13258

Disable the Rails/Delegate cop

Closes #35869

See merge request !13267

Empty project factory by default

See merge request !13260