Add room via space url scheme

[ajbura]

As a room join rule can rely on space and space can have a public join rule, in that case all current matrix.to url scheme fails to offer a easy way to point someone to a room.

matrix.to should offer a way to express that a specific room can be joined with other (space)room.

Current room link url scheme:
https://matrix.to/#/!cURbafjkfsMDVwdRDQ:matrix.org

Example room link via space url scheme
https://matrix.to/#/!cURbafjkfsMDVwdRDQ:matrix.org?viaRoom=#my_space_alias:matrix.org