#1260 Improves/fixes Trivy Stage

[renedupont]

Closes #1260

Notable Changes:

• Enables to use trivy's severity threshold with exit-code option while showing correct bitbucket code insight symbol and keeping report as requested in issue Improve/fix Trivy Stage by being able to use severity thresholds #1260
• Some refactoring including moving code that should be in service layer to TrivyService for better separation of concern
• Fixes bug that exceptions that happen while archiving report to nexus does just return null instead of exception
• Adds a couple of tests to the existing ones
• Renames return code int variable TRIVY_OPERATIONAL_ERROR into TRIVY_FAIL because the scan can now fail due to exceeding the severity threshold as well.