Schedule tests which are known to pass under NoThunks nightly, and the rest monthly

[fraser-iohk]

Description

• Adds a monthly scheduled build as well as the existing nightly scheduled build
• Adds a new matrix variable test-set which determines which set of tests to actually run
  • at the moment, this is either all tests (all) or the test suites which are known to pass under NoThunks (no-thunks-safe)
• Adds a new workflow input nothunks-safe-only which causes a manually-dispatched workflow to use the no-thunks-safe test set
• Adds a new cabal test step which runs the set of NoThunks-safe tests if no-thunks-safe is enabled
• Changes the existing cabal test all step to only run if test-set == 'all'

[jasagredo]

Approving because the comment is not super relevant.