The implicit interface of project services states that the "execute"
method is meant to be called when project hooks are executed.
Currently JiraService does not support any project events even though
JiraService#supported_events says that "commit" and "merge_request"
are supported. They are only used to render correct options in
JIRA configuration screen, but they are not supported.
Because of that, this commit makes "execute" method a no-op.
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.
When a webhook for issues is triggered, it should also return the
resource URL, and the action that was performed (ie: Was it reopened,
updated, opened or closed)
