[fix][java]Add missing generated annotation to Authentication.mustache #900

Job	Run time
Build Java Client JDK8 (samples/client/echo_api/java/resttemplate)	1m 9s
Build Java Client JDK8 (samples/client/echo_api/java/resteasy)	55s
Build Java Client JDK8 (samples/client/echo_api/java/apache-httpclient)	1m 12s
Build Java Client JDK8 (samples/client/echo_api/java/feign-gson)	50s
Build Java Client JDK8 (samples/client/echo_api/java/okhttp-gson)	54s
	5m 0s

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