chore: add Timeout type

[charleenfei]

Description

In many parts of the codebase at the moment, we are always submitting both TimeoutHeight and Timestamp together as params to various functions such as SendPacket, NewPacket, etc.

This PR introduces a new Timeout type containing both the height and timestamp, which we can use to simplify these APIs.

Commit Message / Changelog Entry

imp: adding `Timeout` type to 04-channel which encapsulates both timestamp and block height timeout values

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[damiannolan]

I guess this wasn't generated when QueryTotalEscrowForDenom was added?

[charleenfei]

yea, i think the swagger hadn't been regenerated for a while

[damiannolan]

We could add some extra info to the changelog. E.g.

imp: adding `Timeout` type to 04-channel which encapsulates both timestamp and block height timeout values