update to latest openapi

[giulio-opal]

Could I get a check on this huge update?

Commands run:

cp ../opal/web/backend/router/handlers/public/openapi.yaml api/openapi.yaml
make gen-openapi

Notable changes:

• add templates for the example part of the readme, so that it doesn't get overriden
• add template for github workflow to add an ignore of a failing lint that shouldn't fail. I didn't find anything related about that on openapi-generator, so ignoring is the only way forward
• format all the files with black which is pretty much standard for python (like gofmt)

Evantually I'll set up a github action to automatically release a package on pypi but not in this PR at the moment

To test it do:

pip install git+https://github.com/opalsecurity/opal-python.git@c1d77ff9caf9b85a4c4dec557e3cc986451b412b

[amagnus]

Tested the example from the Readme locally, looks good!

[aashish-opal]

@giulio-opal anything else needed to land this PR?