Create docker image with linux application for headless gif creation

[PlugFox]

Now you can create and save multiple frames only with your browser, platform agnostic
Create a docker image with Linux application for headless gif creation

[creativecreatorormaybenot]

Hi, thanks so much for your contribution! This is already super valuable for anyone wanting to create GIFs with Funvas 🚀

Are you okay with me editing your code once I come back to it? I would leave the PR open for now and the next time I have something to export tackle integrating it.

[PlugFox]

Hi, thanks so much for your contribution! This is already super valuable for anyone wanting to create GIFs with Funvas 🚀

Are you okay with me editing your code once I come back to it? I would leave the PR open for now and the next time I have something to export tackle integrating it.

Of course, anything, do what you want!

This is just proof of concept that everything works fine at any processor architecture (tested on MBR M1 2021 and Hetzner VPS).

[PlugFox]

Also, we should add selecting funvas with an environment variable

e.g.
docker run --env FUNVAS=SOME_NAME ...

import 'dart:io' as io show Platform;

final Funvas funvas = _funvasFromString(io.Platform.environment['FUNVAS'] ?? 'FALLBACK_NAME');