Mark background jobs as time sensitive/insensitive

[ChristophWurst]

This contributes the Calendar part of nextcloud/groupware#28.

Only the hourly sync job is time sensitive, the rest can be done at off times.

method_exists checks will allow us to ship this to older Nextcloud releases.

[codecov]

Codecov Report

Merging #3974 (ab11a08) into main (526b38e) will increase coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##               main    #3974      +/-   ##
============================================
+ Coverage     29.43%   29.44%   +0.01%     
- Complexity      322      323       +1     
============================================
  Files           221      221              
  Lines          7577     7579       +2     
  Branches       1002     1002              
============================================
+ Hits           2230     2232       +2     
  Misses         5347     5347              

Flag	Coverage Δ
javascript	20.81% <ø> (ø)
php	67.40% <ø> (+0.04%)	⬆️

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Impacted Files	Coverage Δ
...r/lib/BackgroundJob/CleanUpOutdatedBookingsJob.php	100.00% <0.00%> (ø)

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