[ADF-2477] message bus in log service (#3063)

* add message bus in log service to allow third pat integrations

* fix test after review

docs/log.service.md

@@ -53,4 +53,36 @@ If you want set for example the log to warning:
 {
     "logLevel": "WARN" 
 }
-```
+```
+
+### Log message bus
+
+The logservice provide also an Observable ***onMessage***  where you can subscribe and recive all the logs: 
+
+The messagge object recived form the bus is composed:
+
+```ts
+{
+    text: "Message log text"
+    type: "ERROR|DEBUG|INFO|LOG|TRACE|WARN|ASSERT"
+}
+```
+ 
+## Usage
+
+```ts
+import { LogService } from '@alfresco/adf-core';
+
+@Component({...})
+export class AppComponent {
+
+    constructor(logService: LogService, myIntegrationService: MyIntegrationService)) {
+    
+        logService.onMessage.subscribe((message) => {
+               myIntegrationService.send(message.text,message.type);
+         });
+                
+    }
+    
+}
+```