Handle unsupported VC aggregation errors better

[corverroos]

Problem to be solved

VCs do not support our proposed aggregation endpoint yet. They do however request and submit aggregations "incorrectly and randomly". This causes weird errors that may be disconcerting and creates noise.

Validator api 5xx response: invalid signature {"status_code": 500, "message": "Internal server error", "duration": "14.387023ms", "vapi_endpoint": "submit_aggregate_and_proofs"}

Proposed solution

Detect unsupported VC calls and improve error logs accordingly.