[DISCUSSION] Deprecate support for Python 3.6

[madpah]

Python 3.6 is reached its end of life as of December 2021.

Questions for open discussion:

1. Should cyclonedx-python-lib continue to provide support for Python 3.6?
2. If Yes to (1), for how long should we look to maintain support for Python 3.6?

FYI: @jkowalleck