Check Scanners At Startup, In Config Tests

[ryanohoro]

Describe the change

work() in strelka.py now calls check_scanners() which attempts to import all scanners enabled in the configuration. Missing scanners will throw ModuleNotFoundError, but any exception will be raised, halting execution when strelka-backend is used.

A test src/python/strelka/tests_configuration/test_scanner_import.py was added that calls check_scanners() when CONFIG_TESTS=true is set.

ScanBITS was throwing an exception and was disabled in backend.yaml until it can be fixed.

ScanRuby was in backend.yaml but does not exist, and was removed.

Describe testing procedures
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Sample output
If this change modifies Strelka's output, then please include a sample of the output here.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of and tested my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings