Enforce ethereum bridge caps

[batconjurer]

While the Ethereum smart contracts should enforce token caps, this should also be enforced namada-side. We should also come up with a strategy for when the are more tokens on the bridge than allowed by the cap (because a cap was lowered).

[sug0]

Regarding:

come up with a strategy for when the are more tokens on the bridge than allowed by the cap

Configuring token caps on the smart contracts can take into account the tokens that are already in circulation. it's worse UX for governance, but whatever.

[sug0]

Regarding the first part, it's a non-issue as well, since token caps are enforced in Ethereum, and a quorum of validators agree on valid events.