relayer V0 command: configuration and parameters

[adizere]

Crate

relayer and relayer-cli

Summary

This is the first iteration on making v0 relayer command more concrete. Currently, the v0 command is almost entirely stubbed, and there is a lot of uncertainty about the types therein.

This work should tackle:

• instantiate ChainRuntime by passing the configuration
• making the types more concrete and filling any gaps or missing pieces, in particular for ChainRuntime, ForeignClient, and ForeignClientConfig.
• bridge the v0 infrastructure with the create_client command -- in this first version we'll probably leave the original create_client implementation untouched (for backwards compatibility with the start command) and simply copy most of that functionality into a new module.
• consider some restructuring, e.g, put ChainRuntime in its own module
• revisit ADR 004 as we go along with this implementation
• _ ... to be decided_

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