[V3] Flatpak for linux distribution

# Feature request

#### Select the type of feature you are requesting:

- [ ] Cog
- [ ] Command
- [ ] API functionality
- [x] Core

#### Describe your requested feature

Distributing through flatpaks would have many benefits even though it may sound stupid at first :
- Distribution agnostic installation
- No Distribution specific issue (example the issue of the Java certificate being wrong on Ubuntu)
- Sandboxing of Java and python which would ensure the correct versions are installed and configured properly
- Updates are streamlined
- Installing multiple versions of red doesn't need any configuration with pyenv or venv

(Snapd or Appimages could also be used potentially to achieve the same results)

The issue names no files, tests, or entry points to begin with. First determine how Red-DiscordBot is currently packaged and released, then define the supported Flatpak scope, runtime dependencies, versioning, and update process before implementation; done means a documented, installable, and maintainable distribution.

Written by the indexing model from the issue text.