feat(modem): method to configure APN/authentication

reach/client/protocol/v2/model/modem.go

@@ -0,0 +1,12 @@
+package model
+
+// type : null, pap_chap, pap, chap
+// if type selected, username and password are mandatory
+type ModemAuthentication struct {
+	Authentication struct {
+		Apn      string `json:"apn"`
+		Type     string `json:"type,omitempty"`
+		Username string `json:"username,omitempty"`
+		Password string `json:"password,omitempty"`
+	} `json:"authentication"`
+}