Set up automated Flux commands reference

[fsteeg]

Like flux-commands.md (which is basically the output of sh flux.sh > flux-commands.md, see metafacture/metafacture-core@4d80ab4), but:

• Improve flux-commands.md content (group commands by type, explain signatures -> Highlight signature of flux-commands metafacture-documentation#16, add missing options) -> Improve Flux HelpPrinter content metafacture-core#367
• Automated creation and publishing of flux-commands.md with GitHub Actions (triggered by metafacture-core releases) -> Automated creation and publishing of flux-commands.md metafacture-core#368
• Add filtering support, e.g. generate filter 'buttons' for each type as input and output, e.g. ->StreamReceiver for all decoders, StreamReceiver-> for all encoders, etc. -> Add filtering support in flux-commands.md metafacture-core#369

[TobiasNx]

Sorting of the list perhaps should be sorted by input not by alphabet.