Create a library for SSVC Calculator

[TG1999]

Currently we have:

vulnerablecode/vulnerabilities/pipelines/v2_importers/vulnrichment_importer.py

Line 215 in be89117

def ssvc_calculator(ssvc_data):

This would be reused at many places, so we should consider moving this as a separate library to avoid code duplication.

[saquibjawedbit]

@TG1999 hey, can i work on this ? can you please assign this to me ?