Fix N+1 query issue in GET /owners endpoint

[shaykeren]

This PR addresses the N+1 query performance issue in the GET /owners endpoint by:

1. Changed pets relationship in Owner entity from EAGER to LAZY fetching
2. Added @batchsize optimization for better performance
3. Updated OwnerRepository with efficient JOIN FETCH queries
4. Maintained backward compatibility

These changes will significantly reduce the number of database queries executed when fetching owners list.

Related issue: #7b3242ee-6c77-11f0-a006-1ac08f985233
Trace ID: 00000000000000004214E9084E40BFF3

Testing:

• Verified reduced query count in logs
• Maintained existing functionality
• Performance improvement confirmed

Please review the changes and test in your environment.