Make publicKey optional when signTransaction

[mjuchli-da]

Make publicKey optional when signTransaction. Instead, some signing providers might want to use the name as an identifier.
Potentially, form a new type KeyIdentifier which holds either a publicKey or the id (or both).

splice-wallet-kernel/api-specs/openrpc-signing-api.json

Line 28 in 71625bd

"publicKey": {

[mjuchli-da]

Hold off until we have a go from blockaemon

[mjuchli-da]

We have the go