Support rename to Permissions-Policy

[adamchainz]

The header is being renamed to Permissions-Policy. See:

• Fixed #30746 -- Added support for Permissions-Policy header. django/django#11735
• https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Feature-Policy
• https://w3c.github.io/webappsec-feature-policy/ - spec was last updated 10 july to say Permissions-Policy

I think we could do a release that adds both Feature-Policy and Permissions-Policy as the headers. Idk about renaming the package.

[ngnpope]

Also note that the syntax of the header value has also changed; see django/django#11735.

[justin-ven]

Would be great to have this feature, even as just a stop-gap until Permissions-Policy is added to Django core (django/django@8bd5b9b)