node declare operator key should be a parameter

[greg-szabo]

The node declare command assumes that the private key held on the file system of the validator server is going to be the operator key for the validator. This is usually not the case in SDK-based chains, because Ledger-based, multisig addresses provide better enterprise-level security for validators.

User story: I would like to use some keystore to store a multisig key and do offline signing of transactions so multisig can be used.

[mappum]

We'll add a few features to address this when reworking the CLI wallet, specifically:

• A flag to support outputting bytes to sign without attempting to sign and submit
• Ledger and multisig support controlled from the CLI wallet