Allow self signed certificate for OpenAPI url

[jasinner]

Is your feature request related to a problem? Please describe.
When trying to generate a Python client using a server which has a self-signed certificate in it's chain there is no option to ignore and generate anyway.

Describe the solution you'd like
Provide an option to ignore self-signed certificate errors such verify=False option in requests library.

Describe alternatives you've considered
Download the file with curl (which doesn't though self-signed cert errors) and load with with --path

[jasinner]

Whoops, duplicate of #531