Enhance signer/signature registration error logs in aggregator

[jpraynaud]

Why

We have noticed during the debugging of bugs that some details are missing in error logs of the aggregator node.

What

Add missing payloads for the signer registration and signature registration when they produce an error.

How

• Add the full content of the payload in the error message of the aggregator:
  • Signer registration
  • Signature registration
• Define some guideline in a dev ADR?