feat: introduce configuration f. SignalinAPI

[paullatzelsperger]

What this PR changes/adds

This PR introduces a configuration module for the Signaling API and it adds it and the data-plane-signaling-api module into a subdirectory.

Why it does that

For some time the SignalingAPI will have to coexist with the ControlAPI, and we must be able to register resources like JSON-LD interceptors,
authentication mechanisms, mappers, etc. separately.

Further notes

.

Linked Issue(s)

Closes # <-- insert Issue number if one exists

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 84.00000% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 73.15%. Comparing base (7f20ba5) to head (efcc243).
Report is 106 commits behind head on main.

Files	Patch %	Lines
...aling/configuration/SignalingApiConfiguration.java	62.50%	3 Missing ⚠️
...figuration/SignalingApiConfigurationExtension.java	94.11%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3938      +/-   ##
==========================================
+ Coverage   71.74%   73.15%   +1.41%     
==========================================
  Files         919      939      +20     
  Lines       18457    18908     +451     
  Branches     1037     1073      +36     
==========================================
+ Hits        13242    13833     +591     
+ Misses       4756     4616     -140     
  Partials      459      459              

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