Notifications: `room_one_to_one` push rule does not consider `m.direct` flag

I'm talking about the following four global push rules (`Underride Rules`):
- ".m.rule.encrypted_room_one_to_one"
- ".m.rule.room_one_to_one"
- ".m.rule.message"
- ".m.rule.encrypted"

For example these rules are visible in the parameters of the Element-web client:


For the end user point of view `one-to-one` refers to the DM (Direct Messages). The problem is the server ignores the actual `m.direct` event defined in the user account data. The server only considers the room members count during the notifications handling.

# Problem:
- If you have a room (not DM) with just 2 people inside it behave from the notification side like a DM
- If you have a DM with more than 2 people inside it behave from the notification side like a group chat

# How it should work for the end user point of view

When sending out notifications the direct message flag should be respected:

* When it is a "normal" room, use notification settings for group chats. No matter if 2, 3 or more people are in the room
* when it is a "DM flagged" room, use notification settings for DM

Start by reading the four named global push rules—.m.rule.encrypted_room_one_to_one, .m.rule.room_one_to_one, .m.rule.message, and .m.rule.encrypted—and how the m.direct account-data event is defined. Done means the specification clearly requires notification handling to respect the direct-message flag rather than room member count, including both two-person rooms and multi-person DMs.

Written by the indexing model from the issue text.