Use v1 and v3 endpoints for /thirdparty tests

[S7evinK]

Updates the endpoints used when testing /thirdparty

[squahtx]

LGTM, but the synapse tests are failing.

Is this blocked on matrix-org/synapse#11158?

[S7evinK]

Yep, this is blocked by that issue.
Keeping unstable in Sytest and using the fallback in Dendrite unfortunately results in Destroying unresponded HTTP request to /appservs/1/_matrix/app/v1/thirdparty/protocol/ymca

[clokep]

I made some more changes, I think pairing this with matrix-org/synapse#15317 will fix the tests.

I also pushed this as a separate branch: https://github.com/matrix-org/sytest/pull/new/clokep/appservice-urls so that the synapse PR picks up these changes via branch matching.

[clokep]

See https://github.com/matrix-org/sytest/actions/runs/4545210009 run against the matching branch.

[clokep]

See matrix-org/sytest/actions/runs/4545210009 run against the matching branch.

This branch (and the Synapse PR) are all green for Synapse.

The PR is all green for Dendrite.

I think this is likely OK to merge?

Note that I just dropped the legacy paths altogether. I think this is OK since they were from before r0.1.0 of the application service spec. (Aka they're ancient.)

I'm going to put this back into the review queue for a double check on my logic.