Reduce sizes of images

[atombender]

The Ubuntu image is 6.5GB (!) compressed. I couldn't even pull this image on my laptop today, since I "only" allocate 45GB to Docker Desktop:

$ docker pull nektos/act-environments-ubuntu:18.04
18.04: Pulling from nektos/act-environments-ubuntu
5c939e3a4d10: Pull complete
c63719cdbe7a: Pull complete
19a861ea6baf: Pull complete
651c9d2d6c4f: Pull complete
8dd387d4677b: Pull complete
2277daa6bda3: Pull complete
44122f010d2c: Pull complete
27df41a4b327: Pull complete
e5e1946d6282: Extracting [==================================================>]  6.592GB/6.592GB
failed to register layer: Error processing tar file(exit status 1): write /usr/lib/x86_64-linux-gnu/libnetsnmpagent.so.30.0.3: no space left on device

Surely it doesn't need to be that huge.

[garthk]

Yeah, nah, to be compatible with any off-the-shelf action you need it has to match the list of everything that GitHub installs for your actions. You can trim the config to just what you need if you learn Packer and build it yourself.