[BAEL-8115] Solving query validation errors for Spring Data JPA

[sdhiray7]

Added the following classes:

• User.java - Entity with escaped reserved keyword (group), proper field-to-column mapping (firstName → first_name), and status field for native query testing
• UserRepository.java - Repository demonstrating three common query validation scenarios and their fixes
• QueryValidationApplication.java - Spring Boot application class to bootstrap the context
• UserRepositoryIntegrationTest.java - Integration tests using @DataJpaTest to validate query correctness at context initialization