[multistage] Handle LiteralOnly query in multistage query

Missing this feature on par with v1.
`SELECT 1;` works,
however
`SELECT 1 from myTable;` will make the whole way to servers.

Start by comparing how v1 handles LiteralOnly queries with the multistage query path, using `SELECT 1;` and `SELECT 1 FROM myTable;` as the behavioral examples. Trace where the latter is sent to servers and determine the expected local handling. Done means multistage matches v1 for both query forms, with coverage for these cases.

Written by the indexing model from the issue text.