chore: issue SEVERE message when no DID value provided

[paullatzelsperger]

What this PR changes/adds

Only a SEVERE warning message is logged when no edc.iam.issuer.id is provided.

Why it does that

Sometimes it is necessary to have a booted runtime, even if it won't be fully operational.

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

Attention: Patch coverage is 50.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 74.02%. Comparing base (7f20ba5) to head (5bf666d).
Report is 179 commits behind head on main.

Files	Patch %	Lines
.../identitytrust/core/IdentityAndTrustExtension.java	50.00%	1 Missing and 1 partial ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4063      +/-   ##
==========================================
+ Coverage   71.74%   74.02%   +2.27%     
==========================================
  Files         919      989      +70     
  Lines       18457    20109    +1652     
  Branches     1037     1126      +89     
==========================================
+ Hits        13242    14885    +1643     
+ Misses       4756     4742      -14     
- Partials      459      482      +23     

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