Update rate limit to use escrowed value across all channels

[nicolaslara]

Background

In the current implementation, native tokens are rate limited based on their total supply. We want them to be rate limited based on the total amount of tokens escrowed across all channels.

Suggested Design

We can implement that by iterating over all the channels and querying their bank balance, but this is inefficient. There is an issue on ibc-go to store this information in state and allow for querying it (cosmos/ibc-go#2664). If that gets accepted, we can implement this by querying that directly.

Alternatively, if there is no interest from the ibc team in having that information be stored in state, we could ask for hooks that allows us to store that ourselves in an accumulator

Acceptance Criteria

Native tokens are rate-limited based on the total amount escrowed across all channels