Cubes using `sql_table` can't be extended with `sql`

[thePermission]

Describe the bug
Hey Guys, i tried to follow:
https://cube.dev/docs/product/data-modeling/concepts/polymorphic-cubes
and
https://cube.dev/docs/product/data-modeling/concepts/code-reusability-extending-cubes
but if you use sql_table in your base cube and sql in your extended cube, then u get the error:
You must use either sql or sqlTable within a model, but not both

To Reproduce

1. Create a Base Cube like this:

cubes:
 - name: users
   sql_table: users

2. Extend the Base Cube like this:

cubes:
  - name: teachers
    extends: users
    sql: >
      SELECT * FROM {users.sql()} WHERE type = 'teacher'
 
  - name: students
    extends: users
    sql: >
      SELECT * FROM {users.sql()} WHERE type = 'student'

Expected behavior
I would expect the sql attribute to overwrite the sql_table

[igorlukanin]

It makes sense to make he sql parameter to supersede the sql_table one. However, I think this is rather a feature request than a bug since a correct error message is provided by Cube now.

[KSDaemon]

Closed via #9386