update agent example for the GenAIComps changes. (#1407)

Update build.yaml and compose_vllm.yaml because of refactoring of GenAIComps.

Fix issue left by https://github.com/opea-project/GenAIExamples/pull/1353

WorkflowExecAgent/docker_compose/intel/cpu/xeon/compose_vllm.yaml

@@ -3,10 +3,10 @@
 
 services:
   worflowexec-agent:
-    image: ${REGISTRY:-opea}/agent-langchain:${TAG:-latest}
+    image: ${REGISTRY:-opea}/agent:${TAG:-latest}
     container_name: workflowexec-agent-endpoint
     volumes:
-      - ${WORKDIR}/GenAIComps/comps/agent/langchain/:/home/user/comps/agent/langchain/
+      - ${WORKDIR}/GenAIComps/comps/agent/src/:/home/user/comps/agent/src/
       - ${TOOLSET_PATH}:/home/user/tools/
     ports:
       - "9090:9090"