chore: add nightly tests against cloud-devel (#1095)

Author: rajatbhatta

.kokoro/nightly/integration-cloud-devel.cfg

@@ -0,0 +1,33 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Configure the docker image for kokoro-trampoline.
+env_vars: {
+  key: "TRAMPOLINE_IMAGE"
+  value: "gcr.io/cloud-devrel-kokoro-resources/java8"
+}
+
+env_vars: {
+  key: "JOB_TYPE"
+  value: "integration-cloud-devel"
+}
+
+# TODO: remove this after we've migrated all tests and scripts
+env_vars: {
+  key: "GCLOUD_PROJECT"
+  value: "span-cloud-testing"
+}
+
+env_vars: {
+  key: "GOOGLE_CLOUD_PROJECT"
+  value: "span-cloud-testing"
+}
+
+env_vars: {
+  key: "GOOGLE_APPLICATION_CREDENTIALS"
+  value: "secret_manager/java-client-testing"
+}
+
+env_vars: {
+  key: "SECRET_MANAGER_KEYS"
+  value: "java-client-testing"
+}