Run Agent E2E tests on triggered Agent builds (#21141)

* Run Agent E2E tests on triggered Agent builds

* Fix comment

Author: Kyle-Neale

.gitlab/build_agent.yaml

@@ -7,9 +7,9 @@
     BUCKET_BRANCH: "dev"
     DEPLOY_AGENT: "false"
     INTEGRATIONS_CORE_VERSION: ${CI_COMMIT_REF_NAME}
-    # disable kitchen and e2e tests
+    RUN_E2E_TESTS: "on"
+    # disable kitchen tests
     RUN_KITCHEN_TESTS: "false"
-    RUN_E2E_TESTS: "off"
   stage: build
   trigger:
     project: DataDog/datadog-agent