Add a helper command line script to merge common forms with bundled XLSForms

[spwoodcock]

Is your feature request related to a problem? Please describe.

• To aid maintainability, the fields common fields across XLSForms have been moved out to xlsforms/common/mandatory_fields.xls and xlsforms/common/digtisation_fields.xls.
• This allows us to inject these fields into each form. So if the fields change, we don't have to update the entire XLSForm library.
• We have a function to do this osm_fieldwork.update_xlsform.append_mandatory_fields.

Describe the solution you'd like

• With this update, the XLSForm library is not usable directly by downloading from the osm-fieldwork repo.
• They must first be ran through the osm_fieldwork.update_xlsform.append_mandatory_fields function.
• We should create a small helper CLI to generate the final XLSForm output for each form in the library.

e.g. something like

xlsform generate --category buildings --output buildings_form.xlsx

• This can be achived using argparse and the scripts part of pyproject.toml, which will output a file to the users bin dir for running the tool.