Rename protobuf Java package (#15658)

Author: andygrove

datafusion/proto/proto/datafusion.proto

@@ -21,7 +21,7 @@ syntax = "proto3";
 package datafusion;
 
 option java_multiple_files = true;
-option java_package = "org.apache.arrow.datafusion.protobuf";
+option java_package = "org.apache.datafusion.protobuf";
 option java_outer_classname = "DatafusionProto";
 
 import "datafusion/proto-common/proto/datafusion_common.proto";