feat: query param to return full state event or event content

query parameter `?format=event|content`

defaults to normal behaviour which is the event's content.

ruma impl: https://github.com/girlbossceo/ruma/commit/788ea6b00fab49b04a17d88caa0c840b7d74aa13



Signed-off-by: strawberry <strawberry@puppygock.gay>