Add form creation

[yanokwa]

I'd love to be able to call a method where I pass in a projectID and a path to an file (XLS or XML) along with ignoreWarnings and publish parameters to programmatically create a form.

I'd expect both of these parameters to default to true because that's my expectation of a form publishing integration, but I'm open to having my mind changed.

I expect the method to set the correct Content-Type based on the file at the path. As we do with pyxform-http, we should set an X-XlsForm-FormId-Fallback to a uuid.

[lognaturel]

Endpoint docs at https://docs.getodk.org/central-api-form-management/#creating-a-new-form

I agree with defaulting ignoreWarnings and publish to true. I don't think we should expose publish at all for now, and we can add it later if it's needed. I think it can be helpful to get warnings, maybe just as a list?

I think ideally there would be one required parameter: a file path. That could be set to an xml, xls or xlsx file. The function would detect the file type and set the Content-Type and X-XlsForm-FormId-Fallback headers appropriately.