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).
issue