Add ability to handle read-only calls on connected chains

[lumtis]

This feature idea is a follow-up of https://github.com/zeta-chain/node/issues/2736 to allow processing results from read only smart contract calls on connected chains.

A new CCTX type should be considered: ReadOnlyCall

The processing would be different here and might be non-trivial to implement, as there will be no receipt hash used as an objective point of observation between the observers.

One solution can be to set in the CCTX object the height of the external chain to be used as a reference for the call. The observer vote for the result at this height.