fix: issue130 Return a 404 error while adding a pet to an unexisting owner

[earlspilner]

Improved handling of 404 errors for non-existing owners and pets in the POST /owners/{ownerId}/pets endpoint. Also switched to using records for error information to simplify and modernize the code.

This PR addresses #130 and enhances both the error handling and the structure of the error responses.

Changes:

1. Fixed the endpoint to return a 404 Not Found status for non-existing owners or pets instead of a 400 Bad Request.
2. Refactored error handling by replacing the previous class-based error representation with Java record, which stands for a more concise and immutable way to handle error details.
3. Few test changes, because the old version was wrong

@arey, please review and merge this update.

[earlspilner]

Okay, finally this build was successful :)
I've made some changes in tests, because from my point there're mistakes

[arey]

Hi @earlspilner
Thank your for your contribution
In the openapi.yaml file, mayve change the Pet not found. by Owner not found?

        404:
          description: Pet not found.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/RestError'

[earlspilner]

In the openapi.yaml file, mayve change the Pet not found. by Owner not found?

I hear you, but here’s the thing — sometimes the issue might not just be with the owner. It could be that neither the ownerId nor the typeId is found in the request. So if we just say "Owner not found," it might not cover all the bases. I’d suggest we go with something like "Pet or Owner not found" to make sure we’re addressing any possible issue that could come up.

[arey]

"Pet or Owner not found"
I'm agree. I didn't think to the pet's type. Good catch.

[earlspilner]

I'm agree. I didn't think to the pet's type. Good catch.

I’ve made the commit and everything’s ready for the merge.

[arey]

All it's ok. Thanks a lot. Feel free to contribute to any other petclinic project / issue.