implement component.evidence.identity

[jkowalleck]

goal: have support for component's identity evidences according to spec https://cyclonedx.org/docs/1.6/json/#components_items_evidence_identity

[indiVar0508]

Hi I am interested to implement this, i see no one is assigned to this
will try to bring up some draft PR asap,
although i notice, there are occurences and callstack also present in doc missing in ComponentEvidence class, do we want to introduce it as part of this issue or already some other issue exists,
for now in draft first will try to get identity up.

[jkowalleck]

feel free to implement everything you need. please keep the pull requests reasonably scoped, so review is easier and features can be released faster.
make sure to add tests for the new structures.