Allow different assets to be on different EVM chains

[Ivshti]

Validator adapter can be made chain agnostic by adding a chain specified in the campaignSpec or even inferring it from the deposit asset. For example, add an optional property depositChainId to the channel schema - if it's not specified, try to infer the chain ID from the depositAsset (token address). Then get an RPC for this chain ID from a configurable list.

Then, the adapter should use this RPC to connect to Ethereum.

The market is agnostic by default (sources data only from the validators), so it shouldn't require any changes.

This way, we can enable campaigns that use xDAI on the xDAI chain, or USDT on BSC, etc.

Chain ids: https://chainid.network/

[Ivshti]

Related:
https://github.com/AdExNetwork/aips/issues/20
#329

[elpiel]

I've started looking into this in Rust, when I finalize the Supermarket I will continue with it.

[elpiel]

channel schema - if it's not specified, try to infer the chain ID from the depositAsset (token address)

After discussing this with @Ivshti , we will drop the inferring of the Chain Id from the depositAsset and use the Ethereum mainnet (chain id 1) by default.
This will remove the need of any validation or pre-processing of the channel (when deserializing with serde) and workarounds. This way the only runtime and configuration checks (e.g. if we are on ENV=production decline any testnet Chain Ids like goerli) will be left to the EthereumAdapter in the Rust implementation as well as linking the Core address for a specific Chain Id.