Update IncomingPhoneNumbers API docs for the status callback feature

This close #2207

Author: gvagenas

restcomm/restcomm.docs/sources-asciidoc/src/main/asciidoc/api/incoming-phone-numbers-api.adoc

@@ -100,6 +100,50 @@ You may specify one or more of the following parameters to update this phone num
 |AccountSid |The unique 34 character id of the account to which you wish to transfer this phone number.
 |==========================================================================================================================================================================================================================================================
 
+[[attributes-status-callback]]
+==== statusCallback
+
+With IncomingPhoneNumber **statusCallback**, you can subscribe to receive webhooks for different events on the incoming phone number.
+
+The statusCallback events are:
+
+ * RINGING
+ * IN_PROGRESS
+ * COMPLETED
+
+==== statusCallbackMethod
+
+The *statusCallbackMethod* attribute allows you to specify which HTTP method Restcomm should use when requesting the URL in the statusCallback attribute. The default is POST.
+
+==== Status Callback HTTP Parameters
+
+The parameters Restcomm passes to your application in its asynchronous request to the StatusCallback URL include all parameters passed in a synchronous request to retrieve RCML when Restcomm receives a call to one of your Restcomm numbers. The full list of parameters and descriptions of each are in the RCML Voice Request documentation.
+
+When the call progress events are fired, the Status Callback request also passes these additional parameters:
+
+[cols=",",options="header",]
+|===================================================================================================================================================================================================================================================================
+|Parameter |Description
+|CallSid |A unique identifier for this call, generated by Restcomm. You can use the `CallSid` to modify the child call by POSTing to Calls/\{CallSid} with a new RCML URL.
+|InstanceId |A unique identifier for this Restcomm-Connect instance.
+|OutboundCallSid | **optional** - A unique identifier for the outbound leg of this call
+|AccountSid | A unique identifier of the account that this number belongs
+|From | A string that describes the From address
+|To | A string that describes the To address
+|CallStatus |A descriptive status for the call. The value is one of **`ringing`**, **`in-progress`**, **`completed`**.
+|ApiVersion | A string that describes the Restcomm-Connect REST API version
+|Direction | A string that describes the direction of the call
+|CallerName | **optional** A string that represents the callers name, if available
+|ForwardedFrom | **optiona** A string that represents the number that the call was forwarded from
+|CallTimestamp | A string the describe the timestamp of the call
+|ReferTarget | **optional** A string that describes the transfer target, if this call started by a transfer
+|Transferor | **optional** A string that describes the transferor, if this call started by a transfer
+|Transferee | **optional** A string that describes the transferee, if this call started by a transfer
+|DialSipCallId | **optional** The SIP Call-ID header value for final SIP Responses to the call
+|DialSipResponseCode | **optional** The SIP response code for final SIP Responses to the call
+|DialSipHeader_ | **optional** The SIP custome headers (if any) for final SIP Responses to the call
+|===================================================================================================================================================================================================================================================================
+
 [[http-delete]]
 ===== HTTP DELETE