Automated creation and publishing of flux-commands.md

[fsteeg]

This is part of metafacture/metafacture.github.io#10

Automated creation and publishing of flux-commands.md (which is basically the output of sh flux.sh > flux-commands.md, see 4d80ab4; Java implementation is in HelpPrinter.java):

• Create flux-commands.md with GitHub Actions (triggered by push to main branch)
• Push flux-commands.md to metafacture.github.io in docs/main with GitHub Actions
• Set up mechanism for release documentation at e.g. docs/5.2.0 & alias docs/latest