Added Variables to Dockerfile

[slycordinator]

• Please check if the PR fulfills these requirements

• [] The changes have been tested locally
• There are no breaking changes

• What kind of change does this PR introduce?
  This change adds variables for the different packages for the docker build.
  It adds variables for the compiler, python, misc, dev, and pip packages to be installed

This separates each of the package categories as well as allows for quickly editing if any packages change. For instance, if alpine were to change the name of a package, replace it with a different one, or if the docker were changed to use a different base distro.

• What is the current behavior?
  There's nothing wrong with the current behavior.

• What is the new behavior (if this is a feature change)?
  The behavior stays the same with this change; this change just makes for easier maintenance.

• Other information:
  This change has the variables in question specified as "ARG". Originally, I used "ENV".
  I made it use ARG, because as I read "ENV" variables are environment variables for the final running container, whereas ARG variables are meant to be used for building a container.

[Ralim]

Hia, can you update this against dev as there are conflicts at the moment.

[slycordinator]

I've updated it to match dev.

black is now in the APK_PYTHON variable and is going to be installed through APK as in the -dev-branch version of the "Dockerfile".