332 add claims supported

[geoff-va]

Completes #332

• Adds OIDC_CLAIMS_SUPPORTED option to oidc settings.py, which defaults to empty list
• Adds claims_supported entry to ProviderInfoEndpoint, retrieved from settings.py
• Added tests for this in test_provider_info_endpoint.py
• Added Docs for entry in settings.rst

[balsdorf]

Thanks for this, it is exactly what I was looking for and planning on implementing. Initial testing works well, will do more thorough testing over the next week. I hope it can be merged in soon.

[JackAtOmenApps]

Awesome enhancement!