feat(IAV-364): Add OAuth validation for HR integrations
- Add token validation responses for Google Calendar, Google Drive, Google Meet, Outlook Calendar, SharePoint, Zoom
- Enhance OAuth service implementation for all HR integration types
- Update OAuth state store for concurrent flow management
- Add OAuth client credentials configuration
- Resolve merge conflicts in OAuthServiceImpl by integrating both upstream and local changes
Related to IAV-364
Closes IAV-364