Issue 20804: Add java nullability annotations (#20806) #664

Job	Run time
Build Java Client JDK17 (samples/client/petstore/java/restclient-swagger2)	1m 38s
Build Java Client JDK17 (samples/client/petstore/java/webclient-useSingleRequestParameter)	1m 28s
Build Java Client JDK17 (samples/client/petstore/java/webclient-jakarta)	1m 24s
Build Java Client JDK17 (samples/client/petstore/java/resttemplate-jakarta)	1m 24s
Build Java Client JDK17 (samples/client/petstore/java/restclient-nullable-arrays)	1m 18s
Build Java Client JDK17 (samples/client/petstore/java/restclient-useSingleRequestParameter)	1m 46s
Build Java Client JDK17 (samples/client/petstore/java/restclient)	1m 37s
	10m 35s

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