Use v3 API for crypto endpoints

[nisbet-hubbard]

Currently, element uses /_matrix/client/r0/keys/signatures/upload instead of the newer and correct /_matrix/client/v3/keys/signatures/upload route. As a result, attempts to set up key backup on the Conduit implementation of Matrix, for example, throw errors.

This has also been documented and fixed for FluffyChat: https://gitlab.com/famedly/fluffychat/-/issues/986.

[Velin92]

Thanks for the feedback, actually I'll propagate this issue in the matrix iOS SDK since there is where the update should be done

[nisbet-hubbard]

Thanks! I’ll keep track over there.