Add ability to be notified on all text messages, but *not* state events

**Is your feature request related to a problem? Please describe.**
Choosing to be notified on "All messages" for a room currently notifies on both text messages and other events such as joins, increasing the badge count for the room (this is describing the behaviour in Element Web/Desktop).


This is a bit awkward from a first-time user experience (FTUE) perspective and is probably not what a typical user would want. This is especially obvious in e.g. company-wide announcement rooms, where you're really only interested in the messages and you want to be notified of messages loudly.

**Describe the solution you'd like**
Since notifying only on messages is achievable with today's push rules, I propose to

1. Rename the current option to something like `All events (messages and state events)`, and
2. Add a new `All messages` option which will only notify on actual messages.

**Describe alternatives you've considered**
Waiting for the new restructured push rules system. That may or may not come, but it's looking like it will not come soon. This proposal is an easy win for usability in the meantime.

The issue identifies no implementation files, tests, or entry points; begin by locating the client notification-setting code and current “All messages” push-rule handling. Done means the existing option distinguishes all events from messages, and a separate option notifies on text messages without state events, with the room badge behavior covered by tests.

Written by the indexing model from the issue text.