This helps when someone just pastes a room alias on the end of the domain,
- `/#room-alias:server` -> `/r/room-alias:server`
- `/r/#room-alias:server/date/2022/10/27` -> `/r/room-alias:server/date/2022/10/27`
Since these redirects happen on the client, we can't write any e2e tests. Those e2e tests do everything but run client-side JavaScript.
Follow-up to https://github.com/matrix-org/matrix-public-archive/pull/107
Part of https://github.com/matrix-org/matrix-public-archive/issues/25
Page-load with the correct homeserver selected (according to `?homeserver`).
Fix https://github.com/matrix-org/matrix-public-archive/issues/92
Also makes sure that the `?homeserver` is always available somewhere in the list; whether that be in the available homeserver list or the added homeserver list depending on it someone cleared it out or never had it because they visited from someone else's link.