[wallets] Implement SignMessage feature in Satoshi Wallet

[bulgakovk]

Satoshi wallet should implement

bitcoin-wallet-standard/packages/core/features/src/signMessage.ts

Lines 17 to 26 in 35e1900

	export type BitcoinSignMessageFeature = {
	/** Name of the feature. */
	readonly [BitcoinSignMessage]: {
	/** Version of the feature implemented by the Wallet. */
	readonly version: BitcoinSignMessageVersion;
	/** Method to call to use the feature. */
	readonly signMessage: BitcoinSignMessageMethod;
	};
	};

for demo purposes