implement POST /_matrix/client/r0/register/msisdn/requestToken
See r.0.6.0 specifications : https://matrix.org/docs/spec/client_server/r0.6.0#post-matrix-client-r0-register-msisdn-requesttoken
See r.0.6.0 specifications : https://matrix.org/docs/spec/client_server/r0.6.0#post-matrix-client-r0-register-msisdn-requesttoken