Install Django and DRF stubs with compatible-mypy extra (as per offical recommendation)

[browniebroke]

Description

Django stubs and DRF stubs are by default leting us install any version of mypy as long as it's not too old. The version restriction can be made more constrained with an extra require specifier.

Checklist:

• I've made sure that tests are updated accordingly (especially if adding or updating a template option)
• I've updated the documentation or confirm that my change doesn't require any updates

Rationale

This might make upgrades more annoying, with the tradeoff that we're more sure to install a compatible version. Overpinning has its drawbacks, especially when the project isn't updated in a timely manner, but these 2 projects are well maintained (at least now). These are optional and could be easily reverted if it's adding too much friction.

[mpsantos]

This will break with mypy 1.3.0 (#4327)

[browniebroke]

Correct, and that's actually the point. Right now, our build doesn't fail and we might ship with a version of mypy which is incompatible with django-stubs. Incompatibilities wouldn't show up on the vanilla project that we generate, but that doesn't mean that a project generated with Cookiecutter Django won't be impacted shortly after, when features start to be added to it.