Defaults for 1:1 chat notifications are not obeyed for Android push notifications

*This issue was originally created by [**@PaulosV**](https://github.com/PaulosV) at .*

### Background information
- **Dendrite version or git SHA**: 0.8.8
- **Monolith or Polylith?**: Monolith
- **SQLite3 or Postgres?**: Postgres
- **Running in Docker?**: Yes
- **Client used (if applicable)**: Element (Android) 1.4.16 [40104162] (G-b8288) ; SchildiChat 1.4.20.sc55 [40100880] (G-776afd86)

### Description

- **What** is the problem: No push notifications are sent for one-to-one chats with room notification settings set to "Default". Defaults for one-to-one chat notifications in Element client are set to "Noisy".
- **Who** is affected: Me.
- **How** is this bug manifesting: On Android, I get no notification for 1:1 chats when the Android app is in the background. I get the notifications when I manually set the chat notifications to "All messages", OR if I set the group messages defaults to "On / Noisy".
- **When** did this first appear: Don't know. Noticed it on 2022-06-19.

### Steps to reproduce

- Login to your Dendrite homeserver on your Android phone.
- In your client, set these defaults in settings - 1:1 chat notifications to On / Noisy, and Group chat notifications to Off.
- Create a 1:1 chat with someone.
- Set room notification settings to Default.
- Ensure that your desktop client is not running / is not in focus.
- Ask the other user to send you a message.

The Android client in the background gets no notification. It should have gotten something. It receives all the notifications when it goes back in the foreground.

No source files, tests, or entry points are named. Start by reproducing the Android background-notification scenario with one-to-one and group defaults, then trace the server-side push notification handling. Done means a one-to-one room using Default follows the client's noisy default while group defaults remain off.

Written by the indexing model from the issue text.