Let `forest-wallet` manage its own wallet

[lemmih]

Issue summary

The Forest node should not have access to sensitive information for security reasons. Messages should be signed by external tools (such as forest-wallet) and handed to the node for inclusion in the blockchain.

• [ ] Use a separate wallet in forest-wallet. This can be implemented without touching the wallet in the Forest node.
• [ ] ~~Add remote commands to forest-wallet for interfacing with a remote wallet (such as a Lotus node).~~
• [ ] Add RPC server that makes a local wallet available remotely. forest-wallet serve.
• [ ] Lock local wallet when in use.
• [ ] Store wallet passwords for, say, 10 minutes after each use.
• [ ] Remove wallet commands from Forest node.

Other information and links

Original issue: https://github.com/ChainSafe/forest/issues/1517

Design discussion: https://github.com/ChainSafe/forest/discussions/2274