Add button to delete all merged branches
## What does this MR do?
It adds a button to the branches page that the user can use to delete all the branches that are already merged. This can be used to clean up all the branches that were forgotten to delete while merging MRs.
**Note**
~~This MR is WIP until MR !6408 is merged.~~
## Are there points in the code the reviewer needs to double check?
The UX of the actual "Delete merged branches" button.
## Why was this MR needed?
Fixes#21076
## Screenshots
Before:
After:
## Does this MR meet the acceptance criteria?
- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support added
- Tests
- [x] Added for this feature/bug
- [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)
## What are the relevant issue numbers?
Closes#21076
See merge request !6449
It adds a button to the branches page that the user can use to delete
all the branches that are already merged. This can be used to clean up
all the branches that were forgotten to delete while merging MRs.
Fixes#21076.
This moves the code used for processing commits from GitPushService to
its own Sidekiq worker: ProcessCommitWorker.
Using a Sidekiq worker allows us to process multiple commits in
parallel. This in turn will lead to issues being closed faster and cross
references being created faster. Furthermore by isolating this code into
a separate class it's easier to test and maintain the code.
The new worker also ensures it can efficiently check which issues can be
closed, without having to run numerous SQL queries for every issue.
Dumping too many jobs in the same queue (e.g. the "default" queue) is a
dangerous setup. Jobs that take a long time to process can effectively
block any other work from being performed given there are enough of
these jobs.
Furthermore it becomes harder to monitor the jobs as a single queue
could contain jobs for different workers. In such a setup the only
reliable way of getting counts per job is to iterate over all jobs in a
queue, which is a rather time consuming process.
By using separate queues for various workers we have better control over
throughput, we can add weight to queues, and we can monitor queues
better. Some workers still use the same queue whenever their work is
related. For example, the various CI pipeline workers use the same
"pipeline" queue.
This commit includes a Rails migration that moves Sidekiq jobs from the
old queues to the new ones. This migration also takes care of doing the
inverse if ever needed. This does require downtime as otherwise new jobs
could be scheduled in the old queues after this migration completes.
This commit also includes an RSpec test that blacklists the use of the
"default" queue and ensures cron workers use the "cronjob" queue.
Fixesgitlab-org/gitlab-ce#23370
