GraphQL API: Add "projects count" and "jobs count" to CiRunner

Description

Users of the runner management UI should be able to see how many:

• Projects (projectCount) are attached to a specific/project runner
• Jobs (jobCount) have run on this runner.

Example:

Questions

• Should users be only able to see projects/jobs they can access or is a total aggregate ok to reveal to any user?
• Counting a large number of items may have performance considerations for large numbers of projects/jobs. Should we return the results up to a maximum? e.g. 1000+ is shown on the pipelines page.

Related (out of scope?)

• Is it useful to filter/segregate failed successful jobs? (e.g. a broken runner would start failing jobs).