Use picocli for parsing action parameters

[rsenden]

Enhancement Request

Fcli actions currently use a custom mechanism for parsing action command-line arguments, handling parameter errors, and generating usage help. It would be great if we can re-use picocli functionality to handle these things, providing much better consistency with regular fcli commands:

• Ability to use the same default values provider, supporting FCLI_DEFAULT_* environment variables for action parameters
• Have picocli generate action usage help
• Have picocli generate synopsis and other information for use in the fcli * action asciidoc commands
• Have picocli handle invalid options (required option missing, unknown options, incorrect values, ...)

More research is needed to see whether this is viable and how to best implement this, but a partial implementation is readily available at https://github.com/fortify/fcli/tree/actions-picocli