Add CustomSql analyzer

Hi all,
Thanks for maintaining this library — it's been very helpful for our data quality project. I would like to propose adding a CustomSql analyzer.

**Is your feature request related to a problem? Please describe.**
The Python version of PyDeequ currently lacks support for the `CustomSql` analyzer available in the Scala version, I could use one on the current data quality project im working on.

**Describe the solution you'd like**
Add a Python wrapper for the existing `CustomSql` analyzer from the Scala implementation.

**Describe alternatives you've considered**
I can't think of any alternatives. The functionality already exists in Scala, and this feature would simply expose it to Python

**Additional context**
I've submitted a pull request with the proposed implementation. Feedback and suggestions are welcome!

Empieza comparando los wrappers de analizadores de Python con el analizador CustomSql existente de Scala y, después, inspecciona cómo las APIs de Python exponen los analizadores de Scala. El trabajo está terminado cuando CustomSql está disponible a través de la Python API, su comportamiento coincide con la implementación de Scala y pasan las pruebas relevantes.

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