Add a field in static chain data describing the way to transport messages with the external chains

[lumtis]

Describe the Issue Currently all chains use the observer/signer set to transport messages with the external chains. As we will enable IBC for some chains, and there might be other different way to transport data, we should describe somewhere what transport method is used.

The best candidate looks to be the chain static data since this information will mostly not chain, IBC chain -> use IBC otherwise use observer/signer.

The idea is to introduce a field like TransportLayer containing the information

Example:

type TransportLayer = OBSERVER | IBC

Ethereum {
  ...
  TransportLayer: OBSERVER
  ...
}
CosmosHub {
  ...
  TransportLayer: IBC
  ...
}