[Anchor] Store the Terra rewards destination address

[ruuda]

We need to store the Terra address where we send the rewards in the UST. For now we opted just for a Solana Pubkey field, but Terra addresses are not the same as Solana ones.

Some resources I was able to find:

• https://docs.rs/cosmwasm-terra/0.7.2/cosmwasm_terra/types/struct.CanonicalAddr.html
• https://docs.cosmos.network/master/basics/accounts.html#keys-accounts-addresses-and-signatures

But in the end, what matters is the format that Wormhole accepts, so we should dive into that.