feat: Add NETCONF OC Pluggable Driver and Mock Server

- Introduced NETCONF_OC_PLUGGABLE driver in ORM_DeviceDriverEnum.
- Enhanced TelemetryBackendService to log device driver and type information.
- Improved DriverInstanceCache to handle connection failures more gracefully.
- Added new telemetry data structure and mock server for optical-channel telemetry.
- Created Dockerfile, docker-compose, and Kubernetes manifests for the NETCONF mock server.
- Implemented test scripts for running and validating the mock server.
- Updated telemetry.json with example optical-channel metrics.
- Refactored existing tests to integrate with the new mock server.