ci: split ci into atomic workflows

[untereiner]

1. Compliance Tests & CPU triggered on builds on a subset of PR events
2. CPU builds triggered on a push on develop or on a workflow call (cf. 1.)
3. GPU builds triggered on a push on develop or on a label event in a PR against develop
4. integrated tests triggered on a label event in a PR against develop
5. code coverage triggered on a label event in a PR against develop

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.39%. Comparing base (0db85be) to head (7462e36).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3266   +/-   ##
========================================
  Coverage    56.39%   56.39%           
========================================
  Files         1065     1065           
  Lines        90326    90326           
========================================
  Hits         50941    50941           
  Misses       39385    39385           

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