Cookiecutter - Support MySQL and custom dockerhub org

[igobranco]

Feature Request

Is your feature request related to a problem or unsupported use case? Please describe.
Currently the CookieCutter doesn't support:

• MySQL instead of PostgreSQL
• custom DockerHub organization, instead of fundocker.

Describe the solution you'd like
Add a question on the CookieCutter that asks the user if he want to support PostgreSQL and/or MySQL;
other Docker Hub organization.

Describe alternatives you've considered
We have been maintain a custom files on .circleci folder on our nau-richie-site-factory, but we want to upstream those custom stuff.

Discovery, Documentation, Adoption, Migration Strategy
Not applicable.

Do you want to work on it through a Pull Request?
@Tiago-Salles will work on this issue.

To see the differences that need to be upstream just compare the .circleci folders of:

• https://github.com/openfun/richie/tree/master/cookiecutter/%7B%7Bcookiecutter.organization%7D%7D-richie-site-factory
• https://github.com/fccn/nau-richie-site-factory/commits/master/