[multistage] attach default limit 10 to queries that doesn't have a limit

- to prevent expensive queries from potentially killing the broker if we do not apply this by default.
- we also need a way to explicitly warn the user the query result is default limited as a warning flag

Start by locating the multistage query path and the broker component that handles queries without an explicit limit. Determine how a default limit and an explicit warning flag could be represented and propagated. Done means unbounded queries receive a limit of 10 and users can tell when that default was applied.

Written by the indexing model from the issue text.