feat: docker images for a provider

[dopry]

Wiring up DOT in a Django instance can be time consuming. Sometimes you just want a simple standalone IDP. I feel it would make DOT more accessible and maybe expand our community.

Describe the solution you'd like
A docker image based on the tests/app/idp

The templates folder should be exposed as a VOLUME.
The setting should use Django-Environ so the instance can be configured using ENV vars passed to the container.

Describe alternatives you've considered
Keycloak - not as easy for me as django/python developer to eject from and customize.
Ory - you need 3 services with their platform (Kratos, Hydra, OathKeeper) and it doesn't really have a UI, DOT + Django wraps up these 3 roles in one service and provides an easy admin interface.

Additional context
Not sure if this would belong with DOT but it would be nice to have it publish in parallel with the same versioning as a sort of 'dogfood/canary' release.

[dopry]

@n2ygk: I was wondering what you thnk of this idea?

[n2ygk]

@dopry sounds like a good idea.