Add generic platform

[last-g]

This offers a generic platform that can be used to easily bootstrap any language or technology.
It provides both build-time extension point and run-time extension point.
It also provides a prepare_build.sh script in attempt to make the build faster and cache friendly.

This is a followup to the discussion in #11

Tested locally:

➜  generic git:(generic_image) docker build .
Sending build context to Docker daemon  8.192kB
Step 1/9 : FROM ubuntu:20.04
 ---> 74435f89ab78
Step 2/9 : RUN apt-get update && apt-get install -y locales     build-essential openssl libssl-dev ca-certificates     && apt-get clean     && rm -rf /var/lib/apt/lists/*     && localedef -i en_US -c -f UTF-8 -A /usr/share/locale/locale.alias en_US.UTF-8
 ---> Using cache
 ---> 48eb127c62ef
Step 3/9 : ENV LANG en_US.utf8
 ---> Using cache
 ---> 1ea6eb467afb
Step 4/9 : WORKDIR /source
 ---> Using cache
 ---> 3523da384f71
Step 5/9 : COPY ./prepare_build.sh .
 ---> b3f9a2d729f8
Step 6/9 : RUN /bin/bash /source/prepare_build.sh
 ---> Running in 2b3dbdc45330
Removing intermediate container 2b3dbdc45330
 ---> 0c68c165efd7
Step 7/9 : COPY . .
 ---> c0f6bd3483cb
Step 8/9 : RUN /bin/bash /source/build.sh
 ---> Running in 53e4646e42e7
Removing intermediate container 53e4646e42e7
 ---> 708c6808d48b
Step 9/9 : ENTRYPOINT ["/bin/bash", "/source/run.sh"]
 ---> Running in bec24911c549
Removing intermediate container bec24911c549
 ---> b11b74861e80
Successfully built b11b74861e80
➜  generic git:(generic_image) docker run -it --rm b11b74861e80 'Whos there?'
Hello, World! and Whos there?

[last-g]

questionable actually

[beevee]

I'm afraid it won't work, because we restrict Internet access during build. apt-get will fail.

You should split your Dockerfile into two separate images:

1. Base image with all necessary dependencies installed (Internet access allowed during build).
2. Runnable image with team's submission (Internet access not allowed during build).

You can refer to a nice working example here: https://github.com/icfpcontest2020/dockerfiles/tree/master/dockerfiles/bazel

[beevee]

Can we close this?