Group Chat Push notifications

[nplasterer]

Push notifications work nearly the same as V2. You will still subscribe to the topic the same way but HMACs are not currently supported. You'll also want to subscribe to the new welcome topic to make sure you get new group chats. /xmtp/mls/1/w-$installationId/proto or use the convinence methods in the code Kotlin -> Topic.userWelcome(installationId)

The new things are

• installationId which you can now get on the client by calling client.installationId
• how to decrypt the message. Now call group.processMessage(encryptedMessageData).decode()

Example push notification server here: https://github.com/xmtp/xmtp-android/blob/main/example/src/main/java/org/xmtp/android/example/pushnotifications/PushNotificationsService.kt

Detailed docs here:
https://github.com/xmtp/xmtp-android/blob/main/library/src/main/java/org/xmtp/android/library/push/README.md

[jhaaaa]

In progress here? #704

[scotboyd]

Addressed in #747