Update Spring Boot Starter to Spring Boot 4 #395

Description

Update the matomo-java-tracker-spring-boot-starter module to support Spring Boot 4.

Tasks

Dependencies

• Update Spring Boot dependency from 3.x to 4.0.5+
• Update related Spring dependencies to compatible versions

Code Changes

• Migrate @NonNull annotation from org.springframework.lang.NonNull to org.jspecify.annotations.NonNull
• Update PropertyMapper usage to align with Spring Boot 4 API (remove alwaysApplyingWhenNonNull())
• Review and update auto-configuration classes for Spring Boot 4 compatibility
• Update filter configuration if needed

Testing

• Run full test suite with Spring Boot 4
• Test auto-configuration functionality
• Test filter integration
• Verify all configuration properties work correctly

Documentation

• Update README.md to reflect Spring Boot 4 requirement
• Update Javadoc if needed
• Add migration notes for users upgrading from Spring Boot 3

Breaking Changes

• Spring Boot 4 is now required (minimum version)
• @NonNull annotation package changed

Acceptance Criteria

• All tests pass with Spring Boot 4
• Auto-configuration works correctly
• No deprecation warnings
• Documentation updated