✨ Add capability to verify signing setup

[Thomasvdam]

✨ Feature

A combination of an endpoint and CLI command to help verify the signing setup of the data proxy.

Motivation

Too often we're running into problems where the proxy signature is invalid, but it's very hard to debug what is going on as you need the overlay node to make a valid request. By adding an endpoint and CLI command to verify the signing setup (excluding upstream calls) we can make it easier to debug and empower Data Proxy operators to independently verify their setup.

Implementation

• Add verification endpoint that generates random data, signs it, and returns it to the client.
• Add a CLI command that takes a verification endpoint, makes a request, and verifies the signature.
• [Optional/Possibly Not Useful] Allow the CLI command to read the private key and sign the same data locally to compare the signature with the received one?
• Document the functionality