Implement sign-to-contract commitments

[dr-orlovsky]

Prerequisites:

• S2C standard Sign-to-contract commitments standards LNP-BP/LNPBPs#118
• S2C commitments in Schnorr signatures inside secp256k1 library.
  Implementation WIP: https://github.com/LNP-BP/secp256k1/tree/schnorr-commitments
  Previous work: Allow sign-to-contract commitments in schnorrsigs [̶a̶l̶t̶e̶r̶n̶a̶t̶i̶v̶e̶]̶ bitcoin-core/secp256k1#589
• S2C commitment scheme for MuSig2 and its implementation in secp256k1-zkp
• Rust code for ECDSA S2C from secp256k1-zkp
• Rust code for Schnorr S2C from secp256k1