feature request: Parsing of command line args as WDL input values

[a-frantz]

This can be added in a follow-up PR to the input module being added in #69 .

miniwdl has this feature and it's very useful for run commands (which does not yet exist in sprocket, but will be added soon). The miniwdl implementation can be reviewed here - https://github.com/chanzuckerberg/miniwdl/blob/main/WDL/CLI.py#L951
miniwdl is able to merge the inputs from a JSON file and the CL, where CL args take precedence and overwrite values present in the JSON. We want to do the same, as that is very handy for scripting.

Primitive type inputs should all be handled in the form <input_key>=<value>. Compound types, structs, and objects, are trickier, and I don't yet know what the most ergonomic CLI would be 🤔

[DeepakSilaych]

can you assign this to me? @a-frantz

[a-frantz]

All yours! I'd recommend brainstorming and getting some feedback in the sprocket slack channel before implementing anything for the compound types, as that might take some workshopping to get right.

[DeepakSilaych]

@a-frantz
should i fork over #69 or base?