Enable read_runner custom ability when user has read_runners ability on the owning group/project

What does this MR do and why?

1. Remove handling of Ci::Runner resource type from Authz::CustomAbility to ensure custom abilities are only checked against a project or a group for which custom roles are assigned.
2. Updates RunnerPolicy to delegate the check if the current user has the read_runners ability on the runner's owning project/group to ProjectPolicy or GroupPolicy depending on the type of the runner

References

Enable read_runner custom ability when user has... (#578173)

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