Determination of the select queries in BaseEngineSpec

[xneg]

Hello!

We are now developing a new SQLAlchemy dialect for Kusto (Azure Data Explorer) and want add support for Kusto database in Superset in nearly future. (This also covers #10646.)
Kusto language has two dialects: SQL and KQL. While there is no problem with SQL dialect, we also want to integrate KQL in Superset.

Problem
KQL select queries do not contain the word "SELECT" so they look like
MyTable | take 10 (this is equivalent of Select * from MyTable Limit 10).
The absence of the "SELECT" keyword breaks the limit behavior in SQLLab because it relies on the sqlparse package and we can't add a limit to queries from UI.

Proposed solution
The solution is to make the determination of the select queries in BaseEngineSpec so that you can override it in your own spec. This is the same way how base dialect determines read-only queries with is_readonly_query.

We will provide PR to implement this small feature.

Thank you!

[xneg]

Closed by #15013