feat: add subject field to comply the change in the azure lib (#71)

It seems that adding a `label` property is no longer supported by the Azure Service Bus library. We have found (not in the documentation) that now the lib is expecting a property called `subject`. 
This change adds a `subject` property next to the existing `label` one (just in case of any potential backwards issue).

lib/operations/topics/publish.js

@@ -14,6 +14,7 @@ module.exports = sender => async (body, options = {}) => { // eslint-disable-lin
 	const { label = '', contentEncoding, applicationProperties, scheduledEnqueueTimeUtc, ...messageFields } = options;
 	const message = {
 		label,
+		subject: label,
 		applicationProperties: {
 			contentEncoding,
 			attemptCount: 0,

package.json

@@ -1,6 +1,6 @@
 {
   "name": "systemic-azure-bus",
-  "version": "3.3.3",
+  "version": "3.4.0",
   "description": "A systemic component for azure bus",
   "main": "index.js",
   "scripts": {