fixes #14415 - check CR availability with Fog, not SETTINGS
Simplifies the code for checking compute resource availability, which can easily be determined with the registered Fog providers instead of being stored in SETTINGS in app initialisation. Plugins should always be loaded, so should not need to override this class method.
Related issues
Refactor #14415: Replace use of SETTINGS to check compute resource availability
fixes #14415 - check CR availability with Fog, not SETTINGS
Simplifies the code for checking compute resource availability, which
can easily be determined with the registered Fog providers instead of
being stored in SETTINGS in app initialisation. Plugins should always be
loaded, so should not need to override this class method.