Set up code migration tests

[stiiifff]

Quoting original issue #180 :

Set up tests to simulate hypothetical situations where code migration would be needed to recover the funds from any
contract. this will likely involve extending contracts with a new method that would recover the funds to a specified address, migrating the contract, and asserting that everything goes well.

Closing criteria (applies per contract):

• unit tests for migrations
• mainnet test for migration
• local interchain test for migration (nice to have)

[bekauz]

this branch contains our latest release contracts with an additional RecoverFunds { denoms: Vec<String> } execute msg variant.

with that branch we can deploy both pre- and post-migration contracts, perform the code migrations, and execute the newly added methods in our unit tests.