feat: add alias for issuance date

[paullatzelsperger]

What this PR changes/adds

Adds a JSON alias validFrom for the issuance date of a VerifiableCredential to compensate a vagueness in the StatusList2021 spec:

• VC Datamodel 1.1 requires a issuanceDate field
• VC Datamodel 2.0 requires a validFrom field
• StatusList2021 explicitly mentions the VC Datamodel 1.1 as normative reference
• StatusList2021 requires a validFrom field, which would violate the previous spec
• StatusList2021 uses yet another option, an issued field in its examples

This is quite inconsistent, and so far EDC could accomodate issuanceDate and issued, but not validFrom. This PR changes that.

Why it does that

VCs are not always parsed using the Json-LD transformers: when we fetch a StatusList2021Credential it is parsed using standard Jackson features.

Further notes

List other areas of code that have changed but are not necessarily linked to the main feature. This could be method
signature changes, package declarations, bugs that were encountered and were fixed inline, etc.

Linked Issue(s)

Closes # <-- insert Issue number if one exists

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.03%. Comparing base (7f20ba5) to head (37f6e54).
Report is 297 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4254      +/-   ##
==========================================
+ Coverage   71.74%   75.03%   +3.28%     
==========================================
  Files         919     1046     +127     
  Lines       18457    20980    +2523     
  Branches     1037     1169     +132     
==========================================
+ Hits        13242    15742    +2500     
+ Misses       4756     4726      -30     
- Partials      459      512      +53     

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