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!

Beginne damit, die Python-Analyzer-Wrapper mit dem bestehenden Scala-CustomSql-Analyzer zu vergleichen, und untersuche dann, wie Python-APIs Scala-Analyzer verfügbar machen. Erledigt ist die Aufgabe, wenn CustomSql über die Python API verfügbar ist, sich wie die Scala-Implementierung verhält und die relevanten Tests bestehen.

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