Add pods/exec as something gitlab needs if RBAC is enabled. Since we...

What does this MR do?

Edits the comments in the values.yaml documenting the required RBAC permissions for making gitlab runner work successfully.

Why was this MR needed?

We chased our tails quite a bit before finding it - probably because we copypasted the example.

What's the best way to test this MR?

Have a locked down cluster with RBAC enabled, run the gitlab runner. If you've successfully duplicated our environment, pods will go into RUNNING and everything will look fine. However gitlab will never see the runners as RUNNING and will timeout waiting for jobs to launch.

Checking the pod named gitlab-runner logs, you will see something like:

...cannot create resource pods/exec in the API group "" in the namespace ...

Adding pods/exec fixes this.

What are the relevant issue numbers?

Kinda sorta maybe: gitlab-org/gitlab-runner#29351 (closed)