Add XML configuration files and tests for DSCM pluggables for ECOC2026 Demo (Proteus-6G)

- Introduced `edit_dscm_hub.xml` and `edit_dscm_leaves.xml` for hub and leaf configurations.
- Added `run_ecoc26_test.sh` script to automate test execution with coverage measurement.
- Implemented `test_ecoc26.py` for end-to-end testing of the DSCM pluggables flow.
- Developed `test_ecoc26_messages.py` for generating HTTP JSON payloads and gRPC proto messages.
- Added `test_ecoc26_xml_capture.py` to render and validate NETCONF XML configurations for hub and leaf pluggables.