After the `IndexTemplateRegistry` was made project-aware in #126986,
we were seeing timeouts of the MP version of the x-pack YAML test suite.
The original version has a timeout of 60 minutes but the MP-version
still had a timeout of 30 minutes. We've gotten away with that
difference because there are still tests on the blacklist for the MP
version, but now that we're making more and more features project-aware,
we need to align the timeout.
Fixes#127433
In the multi-project yaml rest tests, switch to using the routing table
(from cluster state, see MP-1695) to determine that the projects have been
correctly created and configured in the test client.
