Log task event handlers as INFO.

[hjoliver]

At the moment, event handlers only show up below DEBUG level if they fail. Which is annoying.

On this branch:

 $ cylc log junk | grep Event
2023-12-18T17:17:59+13:00 INFO - Event 1/foo/01 "failed" event-handler-00: cylc set-outputs junk/run168//1/foo
2023-12-18T17:17:59+13:00 INFO - Event 1/bar/01 "failed" event-handler-00: cylc set-it-alight -o succeeded junk/run168//1/bar
2023-12-18T17:18:00+13:00 INFO - Event 1/foo/01 "failed" event-handler-00: succeeded
2023-12-18T17:18:00+13:00 WARNING - Event 1/bar/01 "failed" event-handler-00: failed

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• [*] 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.