Ics20Withdrawal packet-forwarding middleware support

[aubrika]

via Gabe:

The web team wants to build an "unshield page" in the Dex Explorer v2 that uses the Skip API to "unwind" tokens automatically to the users chosen destination.

At the moment, users cannot do an Ics20Withdraw for say $TIA from Penumbra to Osmosis in one transaction. They are required to do: Penumbra -> Celestia -> Osmosis. Given ibc transfer paths creates new token denoms, all cosmos projects choose to "unwind" through the native chain. If the chains in this path have "packet forward middleware", then this process is easy for the user and does not require signatures on multiple chains.

To note:

• [ ] The memo message should be compatible with what the message the Skip API provides (https://docs.skip.build/go/general/getting-started)
• [ ] Should review https://github.com/cosmos/ibc-apps/tree/main/middleware/packet-forward-middleware

Acceptance criteria:

• [ ] Should be able to take a message from Skip, put it in the memo field, and issue an Ics20Withdrawal with the unwinding happening successfully.