chore: dedicated class for default JwsSignerProvider

[paullatzelsperger]

What this PR changes/adds

provide a dedicated class for the default JwsSignerProvider

Why it does that

avoid code duplication

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]

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Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.

Project coverage is 74.96%. Comparing base (7f20ba5) to head (b93e15b).
Report is 428 commits behind head on main.

Files with missing lines	Patch %	Lines
...c/security/token/jwt/DefaultJwsSignerProvider.java	0.00%	5 Missing ⚠️
.../org/eclipse/edc/token/TokenServicesExtension.java	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4403      +/-   ##
==========================================
+ Coverage   71.74%   74.96%   +3.21%     
==========================================
  Files         919     1073     +154     
  Lines       18457    21459    +3002     
  Branches     1037     1171     +134     
==========================================
+ Hits        13242    16086    +2844     
- Misses       4756     4852      +96     
- Partials      459      521      +62     

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