Rephrase error messages in logical planner for unsupported features

Some of the unsupported features in logical planner are supported if the query is router plannable. But yet we still report those are not supported.

Some examples are subqueries, CTEs, windows functions, outer joins etc. We do support them for router plannable queries. Perhaps we should rephrase error hints to suggest that feature is supported if the query was router plannable.

Start in the logical planner's unsupported-feature error handling and compare the messages for subqueries, CTEs, window functions, and outer joins with router-plannable queries. Done means the error hints accurately explain when each feature is supported; the issue does not name specific files or tests.

Written by the indexing model from the issue text.