Further log tidy

[oliver-sanders]

Built on #5081
Addresses #3647

Follow on from #5081, tidy up some additional logging.

1. Remove the "CRITICAL" log message for failed tasks.
   • Task failure is logged either two or three times.
   • If the failure is a problem we will get a "did not complete required outputs" message at a higher level.

 2022-09-29T08:49:27Z INFO - [20191209T1200Z/foot running job:01 flows:1] => failed
-2022-09-29T08:49:27Z CRITICAL - [20191209T1200Z/foot failed job:01 flows:1] failed
 2022-09-29T08:49:27Z WARNING - [20191209T1200Z/foot failed job:01 flows:1] did not complete required outputs: ['succeeded']

2. Bump "Incomplete tasks" messages from WARNING to ERROR
   • Incomplete outputs require operator intervention to overcome.
   • This represents an error in graph execution.
   • This should be made prominent in the GUI.

- 2022-09-29T08:49:27Z WARNING - [20191209T1200Z/foot failed job:01 flows:1] did not complete required outputs: ['succeeded']
+ 2022-09-29T08:49:27Z ERROR - [20191209T1200Z/foot failed job:01 flows:1] did not complete required outputs: ['succeeded']

3. Demote "spawned" message from INFO to DEBUG
   • Task spawning isn't really a user-facing concept, it's an internal implementation detail.
   • Spawned tasks will immediately omit a => waiting message anyway so it's duplicate information.

-2022-09-29T08:49:27Z INFO - [20191209T0900Z/foo_start waiting(runahead) job:00 flows:1] spawned
 2022-09-29T08:49:27Z INFO - [20191209T0900Z/foo_start waiting(runahead) job:00 flows:1] => waiting

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.
• Tests are included (or explain why tests are not needed).
• CHANGES.md 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, PRs raised to both master and the relevant maintenance branch.

[hjoliver]

LGTM. Significantly cleaner log files now 👍

I'll apply the small test fix to the branch myself, and merge. One review will do (it only affects logs...)