Update  API spec files to describe the correct class by changing `API::API` to the corresponding class, for example `API::AwardEmoji`.

Closes #24902

See merge request !7718

Pass commit data to ProcessCommitWorker

This changes `ProcessCommitWorker` so that it takes a Hash containing commit data instead of a commit SHA. This means the worker doesn't have to access Git just to process a commit message (and other data it may use). This in turn should solve the problem of ending up with 15 000-something jobs in the `process_commit` queue that take forever to process.

See merge request !7744

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

By passing commit data to this worker we remove the need for querying
the Git repository for every job. This in turn reduces the time spent
processing each job.

The migration included migrates jobs from the old format to the new
format. For this to work properly it requires downtime as otherwise
workers may start producing errors until they're using a newer version
of the worker code.

API: Expose branch status

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/24938

See merge request !7796

Grapify the projects API

Related to #22928 

See merge request !7456

Rename `MergeRequest#pipeline` to `head_pipeline`

## What does this MR do?

This MR renames `MergeRequest#pipeline` to `MergeRequest#head_pipeline`

## Does this MR meet the acceptance criteria?

- [x] All builds are passing

## What are the relevant issue numbers?

Closes #24810

See merge request !7783

Sorting by created_at can lead to uncertainties if two records are
created at the same time.

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