feat: move key-related classes into a separate SPI and Lib module

[jimmarino]

What this PR changes/adds

This PR moves key-related interfaces and classes into their own SPI and Lib modules so that they are isolated from the core connector implementation.

Linked Issue(s)

Part of #4028

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 20.00000% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 74.03%. Comparing base (7f20ba5) to head (2a98e38).
Report is 161 commits behind head on main.

Files	Patch %	Lines
...ava/org/eclipse/edc/keys/keyparsers/JwkParser.java	20.00%	4 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4038      +/-   ##
==========================================
+ Coverage   71.74%   74.03%   +2.28%     
==========================================
  Files         919      989      +70     
  Lines       18457    20053    +1596     
  Branches     1037     1126      +89     
==========================================
+ Hits        13242    14846    +1604     
+ Misses       4756     4726      -30     
- Partials      459      481      +22     

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