the solution of TESB-10959 for sam-agent

1) make "EventFeature" a interface
2) create a new class named "EventFeatureImpl" which "extends AbstractFeature implements EventFeature"

Nothing need to be changed for existing CXF services/clients with sam enabled.
<osgi:reference id="eventFeature" interface="org.talend.esb.sam.agent.feature.EventFeature" />
or:
<jaxws:features>
    <ref bean="eventFeature"/>
</jaxws:features>