Add comprehensive Postman test collection for USE Web API

[Copilot]

Adds a new comprehensive Postman test collection to thoroughly test the USE Web API endpoints with correct HTTP status code expectations.

Changes

• New test collection: use-webapi-comprehensive.postman_collection.json with 40+ test cases covering:
  • Model CRUD (create, get by name, get all, duplicate handling)
  • Class operations (create, get, validation errors)
  • Attribute operations (add, get by name, invalid type handling)
  • Operation/method management
  • Association creation and retrieval
  • Invariant and pre/post condition operations
  • Error handling (malformed JSON, empty bodies, missing headers)
  • Performance benchmarks

Expected Status Codes

Scenario	Status Code
Successful POST	201 Created
Successful GET	200 OK
Duplicate key	409 Conflict
Not found / validation error	400 Bad Request

HATEOAS validation intentionally omitted per requirements (still WIP).

Original prompt

in the use_api package create more postman test like in the json here use-api/src/it/java/org.tzi.use/postman_collection for the api and test different cases, add them into an extra json file next to it.
Reuse the already given tests and improve upon them.
Test it thoroughly, I might have used the wrong HTTP response code, when testing expect the correct one in that context and I will see my mistakes better.

Dont do any hateoas validation for now that part is still a work in progress so alot is going to change.

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[husakki]

Was done manually here 0baa88b