[ONOS-6699] Add ApplicationState enum type in protobuf model

Change-Id: I4315ea7b7207d42a4404ca2795a1891c4ac80b28
diff --git a/incubator/protobuf/models/src/main/proto/app/ApplicationEnumsProto.proto b/incubator/protobuf/models/src/main/proto/app/ApplicationEnumsProto.proto
new file mode 100644
index 0000000..a61e046
--- /dev/null
+++ b/incubator/protobuf/models/src/main/proto/app/ApplicationEnumsProto.proto
@@ -0,0 +1,11 @@
+syntax = "proto3";
+option java_package = "org.onosproject.grpc.app.models";
+
+package app;
+
+enum ApplicationStateProto {
+    // Indicates that application has been installed, but is not running.
+    INSTALLED = 0;
+    // Indicates that application is active.
+    ACTIVE = 1;
+}
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