Standardize branch name params as `branch` on V4 API

Closes #22132

See merge request !8936

API: Make subscription API more RESTfuL

Closes #28327

See merge request !9325

Create compare object with default branch when target branch is missing

Closes #28051

See merge request !9263

Spam check and reCAPTCHA improvements

Closes #28093

See merge request !9248

fixes delimiter removes when todo marked as done

Closes #28462

See merge request !9435

Fix form response errors not shown for create label dropdown.

See merge request !9058

Add filtered search to MR page

Closes #27131

See merge request !9284

No more and/or

See merge request !9428

Copy data before compression to prevent 'file changed as we read it'

Closes #26881

See merge request !8728

#26703 change todos counter position & format ( for large counts )

Closes #26703

See merge request !9171

# This is the 1st commit message:

Add `copy` backup strategy to combat file changed errors

The backup Rake task used to stream data directly from the live
data directory into the backup. Under many circumstances this worked
OK. However, really active instances would experience a 'file changed
as we read it' error - especially with data like the registry. This
now copies the data first, then compresses it. It will take a bit
more disk space while the backup is in progress, but it's a
necessary thing.

# The commit message #2 will be skipped:

#	Add env var

Redo internals of Incoming Mail Support

See merge request !9385

Fix the commit search UI

Closes gitlab-ee#1765

See merge request !9411

Upgrade Rails to 4.2.8

See merge request !9419

Rename retry failed button on pipeline page to just retry

See merge request !9369

Add user deletion permission check in `Users::DestroyService`

See merge request !8974

Changed coverage reg expression placeholder text to be more like a placeholder

Closes #28389

See merge request !9407

Hash concurrent foreign key names similar to Rails

See merge request !9415

Fix preselected namespace when creating a project

Closes #26879

See merge request !9389

Use POST methods to mark Todos as done

Closes #28467

See merge request !9410

Update using_docker_images.md

See merge request !9417

Added ability to change user permissions in group to owner

Closes #28233

See merge request !9299

Fixed alignment of snippet search results

Closes #26832

See merge request !9228

Signed-off-by: Rémy Coutable <remy@rymai.me>

This was initially not implemented simply because I forgot about the
size limit of constraint names in PostgreSQL (63 bytes). Using the old
technique we can't add foreign keys for certain tables. For example,
adding a foreign key on
protected_branch_merge_access_levels.protected_branch_id would lead to
the following key name:

    fk_protected_branch_merge_access_levels_protected_branches_protected_branch_id

This key is 78 bytes long, thus violating the PostgreSQL size
requirements.

The hashing strategy is copied from Rails' foreign_key_name() method,
which unfortunately is private and subject to change without notice.