'cylc show': display state attributes and flows

[hjoliver]

Extend cylc show to display state attributes (queued, held, runahead) and flow numbers (if not just flow 1).

Close #6490

e.g.:

description: (not given)
URL: (not given)
state: waiting (held,runahead)  # <-----(new)
flows: [1,2]                    # <-----(new)
prerequisites: (None)
outputs: ('⨯': not completed)
...

Check List

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Applied any dependency changes to both setup.cfg (and conda-environment.yml if present).
• Tests are included (or explain why tests are not needed).
• Changelog entry included if this is a change that can affect users
• Cylc-Doc pull request opened if required at cylc/cylc-doc/pull/XXXX.
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[dwsutherland]

LGTM 👍