Add GRPC proto submodules

.gitmodules

@@ -0,0 +1,12 @@
+[submodule "proto/data-plane-api"]
+	path = proto/data-plane-api
+	url = https://github.com/envoyproxy/data-plane-api.git
+[submodule "proto/udpa"]
+	path = proto/udpa
+	url = https://github.com/cncf/udpa.git
+[submodule "proto/protoc-gen-validate"]
+	path = proto/protoc-gen-validate
+	url = https://github.com/envoyproxy/protoc-gen-validate.git
+[submodule "proto/googleapis"]
+	path = proto/googleapis
+	url = https://github.com/googleapis/googleapis.git

cloudbuild.yaml

@@ -13,6 +13,20 @@
 # limitations under the License.
 
 steps:
+  - name: gcr.io/cloud-builders/git
+    entrypoint: '/bin/sh'
+    args:
+    - '-c'
+    - |
+      git clone --depth 100 https://github.com/envoyproxy/data-plane-api.git proto/data-plane-api
+      git -C proto/data-plane-api checkout b84d3bea45b59abc3fd21fba26140a379461fc67
+      git clone --depth 100 https://github.com/cncf/udpa.git proto/udpa
+      git -C proto/udpa checkout efcf912fb35470672231c7b7bef620f3d17f655a
+      git clone --depth 100 https://github.com/envoyproxy/protoc-gen-validate.git proto/protoc-gen-validate
+      git -C proto/protoc-gen-validate checkout e84d38a1a4c27d4662779c31a06528cdbc6b4b4f
+      git clone --depth 100 https://github.com/googleapis/googleapis.git proto/googleapis
+      git -C proto/googleapis checkout 2db5725bf898b544a0cf951e1694d3b0fce5eda3
+    id: fetch-git-submodules
   # clippy tends to rely on cached results from other cargo sub-commands so
   # that it skips checking some files that were built previously. As a result
   # we run it before other cargo sub-commands to ensure that it checks all files.