add grpc-dotnet to stable GKE benchmarks (#29369)

tools/internal_ci/linux/grpc_e2e_performance_gke.sh

@@ -52,6 +52,7 @@ if [[ "${KOKORO_GITHUB_COMMIT_URL%/*}" == "https://github.com/grpc/grpc/commit"
 else
     GRPC_CORE_GITREF="$(git ls-remote https://github.com/grpc/grpc.git master | cut -f1)"
 fi
+GRPC_DOTNET_GITREF="$(git ls-remote https://github.com/grpc/grpc-dotnet.git master | cut -f1)"
 GRPC_GO_GITREF="$(git ls-remote https://github.com/grpc/grpc-go.git master | cut -f1)"
 GRPC_JAVA_GITREF="$(git ls-remote https://github.com/grpc/grpc-java.git master | cut -f1)"
 # Kokoro jobs run on dedicated pools.
@@ -99,8 +100,8 @@ buildConfigs() {
         -o "loadtest_with_prebuilt_workers_${pool}.yaml"
 }
 
-buildConfigs "${WORKER_POOL_8CORE}" "${BIGQUERY_TABLE_8CORE}" -l c++ -l csharp -l go -l java -l php7 -l php7_protobuf_c -l python -l ruby
-buildConfigs "${WORKER_POOL_32CORE}" "${BIGQUERY_TABLE_32CORE}" -l c++ -l csharp -l go -l java
+buildConfigs "${WORKER_POOL_8CORE}" "${BIGQUERY_TABLE_8CORE}" -l c++ -l csharp -l dotnet -l go -l java -l php7 -l php7_protobuf_c -l python -l ruby
+buildConfigs "${WORKER_POOL_32CORE}" "${BIGQUERY_TABLE_32CORE}" -l c++ -l csharp -l dotnet -l go -l java
 
 # Delete prebuilt images on exit.
 deleteImages() {
@@ -115,6 +116,7 @@ trap deleteImages EXIT
 time ../test-infra/bin/prepare_prebuilt_workers \
     -l "cxx:${GRPC_CORE_GITREF}" \
     -l "csharp:${GRPC_CORE_GITREF}" \
+    -l "dotnet:${GRPC_DOTNET_GITREF}" \
     -l "go:${GRPC_GO_GITREF}" \
     -l "java:${GRPC_JAVA_GITREF}" \
     -l "php7:${GRPC_CORE_GITREF}" \