Refactor DSCM REST API to integrate Pluggables service

- Updated routes.py to implement GET, POST, and DELETE methods for managing pluggables.
- Introduced JSON to Proto conversion functions for creating and configuring pluggables.
- Enhanced error handling and logging for pluggable operations.
- Created new test cases for POST, GET, and DELETE operations on pluggables.
- Added mock web server setup for testing DSCM REST API.
- Implemented unit tests for JSON to Proto conversion functions.
- Added example payloads for hub and leaf configurations in test cases.