Fix matrix api joinRoom() for remote rooms (#60)

When using self-service mode and trying to link with a remote matrix
room (room not in the same HS as the bridge user), then we need to add
the "via" HSs to join the room with, or else it fails.

We get it from the "m.space.child" in the "children_state" of the space
hierarchy.

Co-authored-by: Cadence Ember <cadence@disroot.org>
Reviewed-on: https://gitdab.com/cadence/out-of-your-element/pulls/60
Co-authored-by: Elliu <elliu@hashi.re>
Co-committed-by: Elliu <elliu@hashi.re>

src/types.d.ts

@@ -149,6 +149,14 @@ export namespace Event {
 		prev_content?: any
 	}
 
+	export type StrippedChildStateEvent = {
+		type: string
+		state_key: string
+		sender: string
+		origin_server_ts: number
+		content: any
+	}
+
 	export type M_Room_Message = {
 		msgtype: "m.text" | "m.emote"
 		body: string
@@ -345,7 +353,7 @@ export namespace R {
 	export type Hierarchy = {
 		avatar_url?: string
 		canonical_alias?: string
-		children_state: {}
+		children_state: Event.StrippedChildStateEvent[]
 		guest_can_join: boolean
 		join_rule?: string
 		name?: string