First attempt at #113: Support help strings for CLI arguments

[csr]

@IamCathal and I are seeking feedback on the code we wrote to get a description of the arguments (original issue: [FEATURE] Support help strings for CLI arguments). This is how we thought about implementing it:

• Add help parameter to Argument, ArgumentInfo, and ParameterInfo classes
• Create a get_arguments_description_from_info function that given an instance of CommandInfo returns an array of descriptions for the ArgumentInfo objects. Each description has the name and the help attributes (how do we get the type out of an annotation object)?

Would this be the right way ahead, or should we look into implementing it using something different? Eventually, we would create a string out of the args_descriptions list and pass it to command.cls(..., help=our_string_here). We also noticed the text that goes into help does get some formatting (leading spaces).

This is obviously not meant to be merged - just looking for initial feedback on code styling ad logic (any feedback is welcome).

[csr]

I'm going to close this as this issue is a little bit more complex than we anticipated. We'll be focusing on [BUG] typer.main.get_group should return a click.Group next.