Display projects related a runner

What does this MR do and why?

This change renders the projects which are linked to a given runner in the runner details page.

Screenshots or screen recordings

New "Assigned Projects" section

How to set up and validate locally

1. With some specific/project runners added (https://docs.gitlab.com/ee/ci/runners/runners_scope.html#specific-runners)

2. In rails console ($ rails c) enable the the view runner page

   Feature.enable(:runner_read_only_admin_view)

3. Visit Admin -> Runners

4. Visit any Project Runner page such as http://gdk.test:3000/admin/runners/108

   1. Optionally edit the Runner to see more or less "Assigned Projects".

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #347856 (closed)