Prepare 7.21.0 snapshot (#22984) #1379

Job	Run time
Build Java Client JDK11 (samples/client/echo_api/java/apache-httpclient)	1m 27s
Build Java Client JDK11 (samples/client/echo_api/java/feign-gson)	1m 7s
Build Java Client JDK11 (samples/client/echo_api/java/resttemplate)	1m 16s
Build Java Client JDK11 (samples/client/echo_api/java/resteasy)	52s
Build Java Client JDK11 (samples/client/echo_api/java/native)	1m 21s
	6m 3s

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