Docs: Review glab runner commands documentation
Review the new `glab runner` command docs to ensure they are consistent with other commands. For example:
- The use of the `-R` and `-repo` options
- Role and permission requirements
## Other links/references
- https://gitlab.com/gitlab-org/cli/-/work_items/8139
- https://gitlab.com/gitlab-org/cli/-/merge_requests/2908
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