Improve CRD validation and configuration initialization logic

[Prajwal-kp-18]

Description This PR improves MeshSync's CRD validation logic by adding strict field validation and implementing default configuration initialization when needed, which enhances reliability during controller reconciliation.

This PR fixes #375

Changes

• Added validation for required fields in MeshSync CRD (spec, watch-list, version)
• Fixed error message capitalization to follow Go conventions
• Implemented default configuration initialization function
• Added comprehensive unit tests for validation logic

Notes for Reviewers

PR Summary

Improved MeshSync’s custom resource validation by adding required field checks and initializing default configurations in the controller’s reconciliation loop.

• [x] Yes, I signed my commits.