Added a getter to OTLA for ObservationRegistry

Author: marcingrzejszczak

micrometer-observation/src/main/java/io/micrometer/observation/contextpropagation/ObservationThreadLocalAccessor.java

@@ -71,6 +71,14 @@ public void setObservationRegistry(ObservationRegistry observationRegistry) {
         this.observationRegistry = observationRegistry;
     }
 
+    /**
+     * Returns the provided {@link ObservationRegistry}.
+     * @return observation registry
+     */
+    public ObservationRegistry getObservationRegistry() {
+        return this.observationRegistry;
+    }
+
     /**
      * Return the singleton instance of this {@link ObservationThreadLocalAccessor}.
      * @return instance