Allow all users to see underlying data with custom SQL dimensions

[ZeRego]

Description

Not developers/admins will get an error when seeing the underlying data of a saved chart that has custom SQL dimension.

This is because the metric query is generated in the FE and passed to the BE.
We need to change the API to build the metric query in the BE so the user can't tamper with the custom SQL.

"Explore from here" and "drill by" buttons should exclude custom SQL dimensions to avoid errors.

What problem does this solve?

Not developers/admins can see the underlying data of a saved chart that has custom SQL dimension.