[AIP-100][Discussion] Introduce private entry function for multisig account creation

[yeptos]

AIP Discussion

This AIP proposes adding new private entry functions to allow an existing Aptos account to create a multisig account using a signer, without requiring complex steps to generate a signature of a struct as proof. Currently, only accounts with Ed25519 and MultiEd25519 authentication schemes can migrate to multisig accounts. This enhancement will enable any account with any authentication key scheme to create a multisig account on top of it, providing a straightforward migration path from any accounts to multisig v2 accounts.

Read more about it here: #496