respect element-call from well-known

[wrenix]

https://github.com/element-hq/element-meta/issues/2371

https://github.com/element-hq/element-x-android/pull/3012

.well-known/element/element.json must be introduced, so Element-X gets the changed server:

{"call":{"widget_url":"https://call.mydomain.com"}}

[SpiritCroc]

I don't touch element call functionality, that's something for upstream

[wrenix]

If i click here i got call.element.io shown, not the one of the homeserver.

Maybe you are correct, is there another indicator which element-call is used?