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!

Inizia confrontando i wrapper degli analyzer Python con l’analyzer CustomSql Scala esistente, quindi esamina come le API Python espongono gli analyzer Scala. Il lavoro è completato quando CustomSql è disponibile tramite la Python API, il suo comportamento corrisponde a quello dell’implementazione Scala e i test pertinenti hanno esito positivo.

Scritto dal modello di indicizzazione a partire dal testo della issue.