End-to-end tests for terraform modules (#1751)

Add end-to-end tests (apply, plan, destroy) for examples.

When run, `tests/examples_e2e`:
1. Create an environment for tests to run (folder, project vpc network) 
2. For each marked example (with `e2e` tftest directive), run apply, plan, destroy
3. Verify:
* no failure in apply
* empty plan after apply
* no failure during destroy
4. When all tests are done, destroy test environment

More details in `tests/examples_e2e/README.md`

tests/modules/cloud_function_v1/assets/sample-function/main.py

@@ -0,0 +1,20 @@
+# Copyright 2023 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import functions_framework
+
+
+@functions_framework.http
+def main(request):
+  return "Hello World!"

tests/modules/cloud_run/examples/simple.yaml

@@ -19,7 +19,7 @@ values:
     metadata:
     - {}
     name: hello
-    project: my-project
+    project: project-id
     template:
     - metadata:
       - {}
@@ -45,7 +45,7 @@ values:
     location: europe-west1
     members:
     - allUsers
-    project: my-project
+    project: project-id
     role: roles/run.invoker
     service: hello