Add documentation for how to use Return type and Read only transactions to create consistent readable state

[theblockstalk]

Documetn how actions can return a type

The docs currently do not show how the ACTION_RETURN_TYPE feature is used to return an object during smart contract execution, either to return it during an API call, or during an inline_action call

I think it should be here: https://docs.eosnetwork.com/docs/latest/smart-contracts/advanced_concepts/

Document how to use query only transaction to return a type

One of the use cases for "Read-Only Transactions" in combination with ACTION_RETURN_TYPE is documented here: EOSIO/eos#9822

It would be good if the documentation could also show how to set up a query-only API call that can be used to return consistent stateful information from several tables at once using these two features