MSC3758: Add `event_property_is` push rule condition kind (#3758)
* Create xxxx-expand-push-rule-conditions.md
* Rename to proper MSC number
* Add PR number to title & wrap
* Remove list matching part of MSC3758, will propose in a new MSC
* Link through to the spec for current match type
* Switch to `value` instead of `pattern` for match key
* Expand missing sections
* Fix typo.
* Clarifications from review.
* Update title in MSC to match PR.
Co-authored-by: Hubert Chathi <hubert@uhoreg.ca>
* Update the name of the push rule condition.
---------
Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>
Co-authored-by: Hubert Chathi <hubert@uhoreg.ca>