feat: add not-equals (!=) operator

[paullatzelsperger]

What this PR changes/adds

Adds the "not-equals" or "!=" operator to our default operator portfolio

Why it does that

General functional completeness, but there is one particular use case: when querying for VerifiableCredentials, we only want those where the status is not "REVOKED" and not "EXPIRED".

If we wanted to "cross all t's and dot all i's" we'd also have to add a "not-in" operator, but this seems good enough for now and keeps the complexity down.

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 #4163

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 74.93%. Comparing base (7f20ba5) to head (655235f).
Report is 243 commits behind head on main.

Files	Patch %	Lines
...lipse/edc/query/CriterionOperatorRegistryImpl.java	50.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4164      +/-   ##
==========================================
+ Coverage   71.74%   74.93%   +3.18%     
==========================================
  Files         919      989      +70     
  Lines       18457    20285    +1828     
  Branches     1037     1146     +109     
==========================================
+ Hits        13242    15200    +1958     
+ Misses       4756     4587     -169     
- Partials      459      498      +39     

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