feat: add signature action to tx button spec

[defispartan]

Add documentation for signature frames as an extension of tx button action.

Additionally, this PR adds two additional fields to untrustedData payload which are used in the tx button lifecycle:

• address : connected wallet address
• transactionId : transaction hash or signed typed data

[neekolas]

FWIW XMTP also has been playing around with signature frames. We just shoved the signature into the transactionId to avoid compatibility issues, which is not beautiful but does maintain compatibility.

Think I'm in complete agreement with @stephancill

[defispartan]

Thanks for the feedback @stephancill @neekola. I think that makes sense to keep using transactionId to avoid a breaking change here, updated the PR.

[stephancill]

@neekolas looks good to go if you're happy!

[lusorio]

Hello, any foreseeable ETA for this?