test(docs-infra): run basic smoke tests against PR previews (#26649)

This makes the tests run agaisnt the deployed production versions (as
part of the `aio_monitoring` job) more reliable.

PR Close #26649

aio/tests/deployment/e2e/protractor.conf.js

@@ -3,9 +3,11 @@
 
 exports.config = {
   allScriptsTimeout: 11000,
-  specs: [
-    './*.e2e-spec.ts'
-  ],
+  suites: {
+    full: './*.e2e-spec.ts',
+    smoke: './smoke-tests.e2e-spec.ts',
+  },
+  suite: 'full',
   capabilities: {
     browserName: 'chrome',
     // For Travis