Python version management

[fbacall]

Some of the python dependencies require python 3.7+

We need a solution for installing the appropriate version of python that may not be available in package repositories. Needs to be integrated into the solution for #1217 to make sure dependencies are installed for correct python version.

We also need to make sure we are consistently using the appropriate version of python when calling out to python from the Rails application.

https://github.com/pyenv/pyenv-virtualenv

[stuzart]

Might be worth looking at the ansible scripts @fherreazcue created. That contains the required packages and versions - https://github.com/seek4science/seek/blob/master/script/ansible/Deploy-SEEK.yml#L152

He uses a separate deadsnakes repo though, which I think we need to careful about and avoid if possible