Mobile app settings backend

[vstpme]

What this PR does

Adds mobile app settings support to OnCall backend.

• Adds a new Django model MobileAppUserSettings to store push notification settings
• Adds a new endpoint /mobile_app/v1/user_settings to fetch/update settings from the mobile app

Some additional info on implementation: at first I wanted to extend the messaging backend system to allow storing / retrieving per-user data and implement mobile app settings based on those changes. After some thought I decided not to extend the messaging backend system and have this as functionality specific to the mobile_app Django app. Currently the messaging backend system is used by the backend and plugin UI, but mobile app settings are specific only to the mobile app and not configurable in the plugin UI.

tldr: wanted to extend messaging backend system, but decided not to do that

Usage

Get settings via API

GET /mobile_app/v1/user_settings
Example response:

{
  "default_notification_sound_name": "default_sound",  # sound name without file extension
  "default_notification_volume_type": "constant",
  "default_notification_volume": 0.8,
  "default_notification_volume_override": false,
  "important_notification_sound_name": "default_sound_important",  # sound name without file extension
  "important_notification_volume_type": "constant",
  "important_notification_volume": 0.8,
  "important_notification_override_dnd": true
}

Update settings via API

PUT /mobile_app/v1/user_settings - see example response above for payload shape.

Note that sound names must be passed without file extension. When sending push notifications, the backend will add .mp3 to sound names and pass it to push notification data for Android. For iOS, sound names will be suffixed with .aiff to be used by APNS.

Get settings from notification data for Android

All the settings from example response will be available in push notification data (along with orgId, alertGroupId, title, etc.).
Fields default_notification_volume, default_notification_volume_override and important_notification_volume , important_notification_override_dnd will be converted to strings due to FCM limitations.
Fields default_notification_sound_name and important_notification_sound_name will be suffixed with .mp3 in push notification data.

iOS limitations

While Android push notifications are handled purely on the mobile app side, iOS notifications are sent via APNS which imposes some limitations.

• Notification volume cannot be overridden for non-critical notifications (so fields default_notification_volume_override and default_notification_volume will be disregarded for iOS notifications)
• It's not possible to control volume type (i.e. "constant" vs "intensifying") via APNS. A possible workaround is to have different sound files for "constant" and "intensifying" and pass that as default_notification_sound_name / important_notification_sound_name.

Which issue(s) this PR fixes

Related to https://github.com/grafana/oncall-private/issues/1602

Checklist

• Tests updated
• No changelog updates since the changes are not user-facing

[matiasb]

LGTM, one minor comment.

[joeyorlando]

lgtm! I'm sure people will be pleased once this is released 😛

[Dieterbe]

since you requested a review, i can say that it looks fine in principle, but obviously i didn' treview the python code.