Explicitly disallow unsupported SQL

[purplefox]

Currently, if a user attempts to create an MV or execute a pull query with unsupported parts of SQL then it will fail in an undefined way.

We should explicitly check after the logical parse stage whether the SQL is supported and return a nice error in case it isn't.

Examples of currently unsupported SQL include:

Pull queries - joins, aggregations, sub queries, some functions Push queries - joins, sub queries, some functions, order by