`@room` push rule doesn't have a sound, which makes it not-noisy

In the [baserules](https://github.com/matrix-org/synapse/blob/605921bc6b3d3f48142e3c8b5ddcc6c2a0016062/synapse/push/baserules.py#L269) and the spec [spec, (goto .m.rule.roomnotif)](https://spec.matrix.org/v1.1/client-server-api/#push-rules) you can see that @room messages are only hightlighted and not noisy by default.

IMHO they are more important than normal room messages and therefore they should be noisy. Moreover they are already shown as noisy in element (probably wrong behavior), but are only highlighted: https://github.com/vector-im/element-web/issues/19750

This behavior becomes really strange if room messages are set to noisy, but @room messages are still quiet.

I can create a pull request to edit the baserules, but maybe some people have other thoughts about that.

Start with the linked m.rule.roomnotif entry in the Matrix client-server specification and compare it with synapse/push/baserules.py at the referenced location. Check how the rule defines highlighting and noise, then determine which specification text or linked implementation behavior must be updated so @room notifications consistently match the intended default.

Written by the indexing model from the issue text.