APNs binary protocol will be disabled in November 2020 - Provide migration steps

[TysonAndre]

https://developer.apple.com/news/?id=11042019a

If you send push notifications with the legacy binary protocol, we recommend updating to the HTTP/2-based APNs provider API as soon as possible. You’ll be able to take advantage of great modern features, such as authentication with a JSON Web Token, improved error messaging, and per-notification feedback.

The Apple Push Notification service (APNs) will no longer support the legacy binary protocol as of November 2020.

• Add startup warnings if anything required to fall back to APNs is missing.
• Update documentation to recommend HTTP2 by default (e.g. warn about missing bundle ids, with instructions on how to add the bundle id to existing psps)
• Look into using HTTP2 by default in new PSPs?
• Update error messages for failing to connect via binary provider API
• Add a way to override the bundleid for individual DPs - this is useful for QA staging builds

See #157