mrgnlabs/marginfi-v2

AI Summary: Implement a new instruction to create Marginfi accounts using Program Derived Addresses (PDAs) instead of keypairs. This involves using seeds including the group, a monotonically increasing u32 counter, and the account's authority. The `transfer_account` instruction should be updated to utilize the PDA method, while maintaining backward compatibility with the existing keypair approach. Consider adding a u32 "id" seed for third-party tagging and potentially restricting certain IDs to specific programs via CPI.