Call handlers when calling sequences from task

Add functionality to call handlers when invoking sequences from tasks.
Add a system property to enable/disable the functionality.
Fixes wso2/product-ei/issues/5226

Author: GDLMadushanka

modules/core/src/main/java/org/apache/synapse/startup/tasks/MessageInjector.java

@@ -36,6 +36,7 @@
 import org.apache.synapse.ManagedLifecycle;
 import org.apache.synapse.MessageContext;
 import org.apache.synapse.SynapseException;
+import org.apache.synapse.SynapseHandler;
 import org.apache.synapse.core.SynapseEnvironment;
 import org.apache.synapse.core.axis2.Axis2SynapseEnvironment;
 import org.apache.synapse.mediators.MediatorFaultHandler;
@@ -96,6 +97,8 @@ public class MessageInjector implements Task, ManagedLifecycle {
     private final static String INJECT_TO_SEQUENCE = "sequence";
     private final static String INJECT_TO_MAIN_SEQ = "main";
 
+    private final static String INJECT_TO_SEQ_FROM_TASK = "tasks.invoke.handlers.when.calling.sequence";
+
     /**
      *  Artifact type which message should be injected
      *  Could be one of "proxy" | "sequence" | "main"
@@ -412,6 +415,18 @@ public void execute() {
                     if (log.isDebugEnabled()) {
                         log.debug("injecting message to sequence : " + sequenceName);
                     }
+                    boolean isInjectToSeq = System.getProperty(INJECT_TO_SEQ_FROM_TASK) != null &&
+                            Boolean.parseBoolean(System.getProperty(INJECT_TO_SEQ_FROM_TASK));
+                    if (isInjectToSeq) {
+                        List handlers = mc.getEnvironment().getSynapseHandlers();
+                        Iterator<SynapseHandler> iterator = handlers.iterator();
+                        while (iterator.hasNext()) {
+                            SynapseHandler handler = iterator.next();
+                            if (!handler.handleRequestInFlow(mc)) {
+                                return;
+                            }
+                        }
+                    }
                     mc.pushFaultHandler(new MediatorFaultHandler(mc.getFaultSequence()));
                     synapseEnvironment.injectAsync(mc, seq);
                 } else {