Handles the signing of a message by displaying a modal for user interaction.
This function opens a modal with the SignMessageModal component, prompting the user to review and approve the message signing request.
Supports signing with any wallet account managed by Turnkey, including externally connected wallets.
Allows for optional overrides of the encoding and hash function used for the payload, enabling advanced use cases or compatibility with specific blockchains.
Optionally displays a subtext in the modal for additional context or instructions to the user.
Returns a promise that resolves to a v1SignRawPayloadResult object containing the signed message, signature, and metadata.