WIP: Add `pipeline show` chat commands
What does this MR do?
This will cover
/gitlab pipeline show <ref> command.
This proposal is here
Screenshots (if relevant)
Does this MR meet the acceptance criteria?
- Changelog entry added
- Documentation created/updated
- API support added
- Added for this feature/bug
- All builds are passing
- Conform by the merge request performance guides
- Conform by the style guides
Branch has no merge conflicts with
master(if it does - rebase it please)
- Squashed related commits together