Planning and execution of SQL queries in QueryEngineRust is limited to those that are strictly equivalent to PromQL #108

We can easily support simple SQL queries that do not have equivalent PromQL.

SELECT <agg>
FROM <table>
WHERE time BETWEEN <start> AND <end>
GROUP BY <columns>

PromQL enforces constraints on <end>-<start> and <columns>, leading to the ONLY_TEMPORAL, ONLY_SPATIAL classification but we don't need to do that for SQL.

We will also need to modify the Controller for this, later.