[TASK] Remote signing interface

[drewstone]

Overview

Operators are likely not thrilled with having keys stored on gadgets/blueprint manager side. There should a plan to leverage AWS KMS for ECDSA as well as a general approach we support for remote signers of arbitrary key types. Eigenlayer is taking this approach too and it should become apart of the SDK imo.

https://github.com/Layr-Labs/cerberus-api