Change Dockerfile base image

[lemonsaurus]

We're currently using alpine for the bot Dockerfile, and it sucks. It's super slow to install the pipenv dependencies, apparently because alpine has a weird C compiler which makes it compile every pip library from scratch instead of using the wheels.

Let's change it to something like minideb or even ubuntu. They're still pretty lean images, but they don't have this problem so build times should be reduced significantly just by using a different image.

[scragly]

https://hub.docker.com/r/bitnami/python/ has started being used for site, which is based on minideb, which is what we will likely go with for this repo also.

[jchristgit]

why not the default python?

[scragly]

Because the default python docker image doesn't have a variant that uses minideb as a base as far as I can tell.

[scragly]

python:3.7-slim does exist though for default python which could be a fine enough alternative. I think it'll be best to just end up comparing build times between the two and picking the fastest one to decide.