Enable ability for smart contracts to be owners of metadata entries.

[SpicyLemon]

Summary

Allow metadata scopes, sessions, and/or records to have owners that are smart contracts.

Problem Definition

As a smart-contract creator, I want to be able to have my smart-contract own metadata entries so I can more easily manage updating information.

Proposal

1. In the x/metadata wasm encoders, add the smart contract address as the first signer of the message being sent.
2. In the x/metadata msg validation, make sure that the first signer is one of the required signers.
3. In our wasmd fork, update handleSdkMessage to only check the first address from GetSigners().

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[SpicyLemon]

It looks like, for 3, we could instead use the WithMessageHandler option and define the handler in the provenance repo instead. Since you've already got it in our wasmd fork, though, we can probably use that just fine. It'd be nice to get off our fork at some point, and go back to using the standard repo. If we ever do that, we'll need to go with the WithMessageHandler way, but until then.... eh.