This adds support for the `build` module for JiraConnect, and
synchronizes pipeline status for linked Jira issues.

Specifically:

- we add a new section to the application descriptor (requiring an
  update of our installed JiraConnect app)
- we add a new worker triggered by changes in status of pipelines
- for every pipeline that is the head-pipeline of a relevant MR
  (determined by the presence of Jira issue keys in either the branch
  name or the title) we send that status information to Jira.

Some notes:

- The concept of a build seems to map most closely to the GitLab concept
  of a pipeline, so that is the unit of synchronization.
- The Jira API allows the number of 'tests' in a build to be reported,
  with a breakdown by pass/fail/skip. Currently this is implemented to
  be the number of Ci::Builds in a pipeline - since we cannot guarantee
  that exact test numbers are available. This may be subject to change,
  or at least upgrade for test frameworks for which we have breakdown
  stats.