Nicer cli help output and generated cli reference

[sh-rp]

Description

• adds rich_argparse to the cli to make the help output nicer (screenshot below)
• adds a dlt command to create a markdown documentation of all the commands on the main argparse
• adds this autogenerated doc output instead of manually kept one at https://deploy-preview-2232--dlt-hub-docs.netlify.app/docs/devel/reference/command-line-interface
• Adds one linter step that ensure the cli docs are up to date

rich_argparse adds 20kb in size, so I think we can keep it in the main dependencies.

[netlify]

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