Implement Tendermint `LightClient`

[ljoss17]

Summary

Building headers for Cosmos chain's is using the LightClient implementation from the current Hermes:

• https://github.com/informalsystems/hermes/blob/v1.7.4/crates/relayer/src/chain/cosmos.rs#L2176
• https://github.com/informalsystems/hermes/blob/v1.7.4/crates/relayer/src/chain/cosmos.rs#L146

Which requires a AnyClientState https://github.com/informalsystems/hermes/blob/v1.7.4/crates/relayer/src/client_state.rs#L50. But the Sovereign Client state only has a TendermintParams field:

• https://github.com/informalsystems/sovereign-ibc/blob/main/clients/sov-celestia/types/src/client_state/definition.rs#L25
• https://github.com/informalsystems/sovereign-ibc/blob/main/clients/sov-celestia/types/src/client_state/definition.rs#L64

Some slight refactoring of the LightClient could allow decoupling it from Cosmos SDK, which would make it possible to build the headers without relying on the current Hermes implementation.

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[thaodt]

hi @ljoss17 can I take this? If yes, my first question is we still keep hermes v1.7.4 version for this feature?

[soareschen]

Hi @thaodt, it might be a little tricky for you to work on this as a first issue, as currently the direction is not very clear on how we should approach this re-implementation.

I have created #214 as an alternative good first issue that you can look into.