Add spec for MSC2449: Require users to have visibility on an event when submitting reports (#1517)

* Add MSC2249 support

* changelog

* Add a line on verification

* Changes based on review feedback

* Apply suggestions from code review

Co-authored-by: Travis Ralston <travpc@gmail.com>

* move tags field to the bottom of report_content.yaml

* fix duplicated content

now how did that happen

* fix up the 404 response schema

it wasn't displaying correctly in the rendered spec otherwise

* remove erroneous schema reference

* 1.7 -> 1.8

Co-authored-by: Travis Ralston <travpc@gmail.com>

---------

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>
Co-authored-by: Travis Ralston <travpc@gmail.com>
Co-authored-by: Andrew Morgan <andrew@amorgan.xyz>

content/client-server-api/modules/report_content.md

@@ -18,3 +18,7 @@ Servers are free to handle the reported content however they desire.
 This may be a dedicated room to alert server administrators to the
 reported content or some other mechanism for notifying the appropriate
 people.
+
+{{< changed-in v="1.8" >}} The server MUST verify that the user 
+reporting the event is currently joined to the room the event is 
+in before accepting a report.