Use configured ChainClient key in tx simulation

[jtieri]

Description

This PR fixes a bug in tx simulation that would present itself in testing due to how the keystore was managed. Instead of trying to read an arbitrary key to get the PubKey details we retrieve the key information for the calling chain's configured key.

Checklist

• I have made sure the upstream branch for this PR is correct
• I have made sure this PR is ready to merge
• I have made sure that I have assigned reviewers related to this project

Testing

There are no specific test cases in the relayer for Evmos and adding some to the relayer is probably more effort than it's worth since we will be ditching the included integration tests in favor of ibctest. Ideally we test EVM based chains in ibctest but that is outside the scope of this work.

• Checkout the relayer at Use updated version of lens cosmos/relayer#779
• Run make test-integration

The tests should all run to completion and pass; before this fix you would see errors like the following

logger.go:130: 2022-06-07T10:52:12.157-0500 INFO    Error building or broadcasting transaction      {"chain_id": "ibc-1", "attempt": 1, "max_attempts": 5, "error": "cannot build signature for simulation, key infos slice is empty"}