Support for extending existing Checks with business specific Checks

**Is your feature request related to a problem? Please describe.**
I would like to be able to add Custom Checks by only making changes in python-deequ and not in deequ (scala). As a team with no Scala knowledge, it would allow for greater efficiency and adoption.

**Describe the solution you'd like**
I'd like to be able to extend Checks with Checks specific to my business that would not be valuable to the community. For example, are the values in a column valid ISBN's?

**Additional context**
If there is a way to do this already, would you mind giving an example and I'll update the docs.

Thanks for your time.

Empieza por leer la Checks API existente y su documentación para determinar si Python ya expone una vía de extensión sin modificar la capa Scala Deequ. Se considera completado si existe un ejemplo documentado solo para Python de un business check, como la validación de ISBN, o una implementación acotada que admita este tipo de checks.

Escrito por el modelo de indexación a partir del texto del issue.