Migrate CLN hold invoices to Boltz hold

[vegita]

Summary

• switch CLN hold invoice calls from the archived holdinvoice RPCs to Boltz hold (Invoice, List, Settle, Cancel)
• load the hold plugin's TLS certs lazily so startup order does not freeze the wrong gRPC credentials
• update gRPC generation and CLN test/development wiring to use Boltz hold v0.3.3
• replace the vendored test plugin binary with the current hold Linux amd64 release binary

Fixes #2317

Verification

• python -m py_compile api\\lightning\\cln.py
• docker compose -f docker-tests.yml --env-file tests/compose.env config --quiet
• generated hold_pb2.py and hold_pb2_grpc.py from the Boltz v0.3.3 proto in a temp venv and validated the expected request fields, RPC methods, and state enum values

I could not run the full Docker integration suite locally because Docker Desktop's Linux engine is not running on this machine (dockerDesktopLinuxEngine pipe is missing).

[vegita]

CI note: the Python lint job passed. Both coordinator test jobs failed before compose/tests at the shared frontend artifact download step (dawidd6/action-download-artifact reports
o downloadable artifacts found (expired) for django-main-static from the Jan 29 run), so those failures do not appear to be from this CLN hold migration.