* Make it easier to mock call memberships for specific user IDs
* Allow sending notification events when starting a call
* rename notify -> notification
* replace `joining` concept with `ownMembership`
* introduce new `m.rtc.notification` event alongside `m.call.notify`
* send new notification event alongside the deprecated one
* Test for new notification event type
* update relation string to match msc
* review
* fix doc errors
* fix tests + format
* remove anything decline related
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Co-authored-by: Timo <toger5@hotmail.de>