… POC

- Read ChainReader config in from RelayConfig
- Add some initialization and validation relay skeletons

- Use medianProviderWrapper instead of passing medianContract separately

This avoids us having to modify the signature of NewMedianFactory, which
would require further modifications to all non-evm repos and chainlink-relay

- Add chain_reader_test.go with some basic relay tests

Co-authored-by: Jordan Krage <[email protected]>

- Add chain reader config validation
- Add chain reader config validation tests
- Add config for chain reader median contract to cr validation testcases
- Add unimplemented Encode(), Decode(), GetMaxEncodingSize(), GetMaxDecodingSize()
- Add ChainReader() method to mock provider for plugin test
- Rename relaymercury.ChainReader to MercuryChainReader, resolve name collisions
- Add tests for errors during ChainReader construction
- Propagate InvalidConfig & any other errors back to client

We should ignore Unimplemented until node ops have been given ample time to migrate to the new job spec
(including a section for ChainReader config) so that we can remove the old product-specific
MedianContract component from MedianProvider. All other errors we can immediately start passing back
to the client, letting the core node decide how to handle them (eg. displaying an "invalid job spec"
message to the UI if the RelayConfig was invalid or the ContractID missing)

…er-EVM-POC

# Conflicts:
#	core/services/ocr2/plugins/ocr2vrf/coordinator/coordinator_test.go