Support MSC4143 RTC Transport endpoint

[Half-Shot]

This implements MSC4143's backend endpoint for transports, and uses matrix-org/matrix-js-sdk#5104 to handle it.

This changes makeTransport to:

• Try all listed transports, not just the first livekit one.
• Test all backend transports, then all well-known transports, then all config transports.

[toger5]

This needs more coverage.
It looks like throwing in a test that uses the new endpoint would get you almost to 100% since it would run thorugh both "throw levels"

[toger5]

This looks sensible.

If one of them fails we always run into a hard error. Do we want automatically check if we suceed in loading one of the lower prio ones?

[Half-Shot]

This needs more coverage. It looks like throwing in a test that uses the new endpoint would get you almost to 100% since it would run thorugh both "throw levels"

Yup! Working through it

[toger5]

In other words: I am not sure if:

Test all backend transports, then all well-known transports, then all config transports.

is actually happening. Are we really continuing to check well-known transports if backend transports fail?
edit
at least in the
ex instanceof FailToGetOpenIdToken case.
edit
Oh which is an issue with our HS and entirely independent of the sfu/jwt.
Liking this more and more while looking into it :)

[Half-Shot]

Oh which is an issue with our HS and entirely independent of the sfu/jwt.
Liking this more and more while looking into it :)

That was my intention yes, but seeing as it wasn't clear this needs more comments on the PR.