To allow Dapps users to sign arbitrary data in the qubic wallet through wallet connect

[sallymoc]

Method name
qubic_sign

Purpose
Allows dApps to request the user to sign a piece of data without sending a transaction to the blockchain.

Usage
The data could be a message or an encoded hash, and the wallet should present this data to the user clearly before signing to ensure they understand what they're signing.

Once the user confirms, the wallet uses the private key of the specified address to sign the message.
The wallet returns the generated signature to the calling dApp.

The signed data can be used for off-chain operations, like proving ownership of an address, authenticating actions, or creating signatures for other applications.