Keyring store directory should be configurable

[soareschen]

Crate

ibc-relayer

Summary

Currently the file-based key ring implementation always store the private keys for relayer wallet at ~/.hermes/keys. This is problematic for testing purposes as the temporary-generated private keys kept piling up at the developer's home directory.

#1521 currently use the in-memory key store to avoid polluting the home directory. However if we want to allow manual invocation of the relayer commands in the middle of the test, the wallet keys have to be exported to the filesystem for the relayer CLI to access it. For now I'd like to avoid exporting the keys to the home directory, and only do file export of keys inside the tests after this issue is resolved.

Proposal

Add a config field in config.toml to specify key store directory.

Acceptance Criteria

Running hermes command with customized config.toml should load wallet keys from directories other than ~/.hermes/keys.

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