Add Multi-Key Support in Custodial Wallet

[p5150j]

Description

Enhance the Custodial wallet to support multiple key types, specifically focusing on adding ETH-compatible keys alongside existing keys.

Tasks

• Design multi-key architecture for Custodial wallet
• Implement storage for multiple key types
• Develop key selection logic for different operations (should default to ETH if exists)
• Implement backup and recovery for multiple keys
• Update security measures for multi-key support

Acceptance Criteria

• [ ] Custodial wallet successfully stores multiple control key types
• [ ] Users can view and manage all their keys
• [ ] Appropriate key automatically selected for each operation
• [ ] Backup and recovery works for all key types
• [ ] Security review completed for multi-key implementation

Engineering Notes

• Apply DB and schema changes to support multiple control keys per account
• Add a new secp256k1 key type for Eth keys