How can we validate that the `subxt::Config` aligns with the chain we're talking to?

We can already validate that the generated subxt interface aligns with the chain we're communicating with. It would be great if there was also a way to validate that the Config implementation we use actually lines up with the chain too.

I think that this can be a part of the problem we're trying to solve in KR2:

Reduce the configuration needed for Subxt to connect to different chains (aim is to make all config discoverable through metadata, but we need to see how much this is possible).

I suspect that the two go hand in hand; if we expose in the metadata enough information to allow us to reduce the params in our config that need hard coding, we'll inevitably also gain some of the information eeded to validate it.

This was initially raised by @smiasojed, who would like to be able to run this check as a part of the cargo contract tool, so eg cargo-contract --config moonbeam can confirm that the moonbean config is appropriate for example.

Start by reading the existing validation for whether the generated Subxt interface aligns with the chain, then inspect how chain metadata and the subxt::Config implementation are represented. Define what metadata can validate and what configuration can be discovered; done means a clear validation path that could support cargo-contract --config moonbeam.