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