feat(generator): generate quickstart scaffold (#7676)

Modify the generator to also create a scaffold for the quickstart
program. Then I used the generator to create the scaffold for the
`logging`, `pubsublite`, `secretmanager`, and `tasks` libraries.

The generated code requires some editing, but these are fairly small.

These quickstarts are compiled in the `cmake-install` build, where we
can compile them in parallel. This was very useful, it found several
bugs in the generated CMake files.

Author: coryan

Diff for: .bazelignore

@@ -7,6 +7,10 @@ cmake-build-release/
 google/cloud/bigquery/quickstart/
 google/cloud/bigtable/quickstart/
 google/cloud/iam/quickstart/
+google/cloud/logging/quickstart/
+google/cloud/pubsublite/quickstart/
 google/cloud/pubsub/quickstart/
+google/cloud/secretmanager/quickstart/
 google/cloud/spanner/quickstart/
 google/cloud/storage/quickstart/
+google/cloud/tasks/quickstart/

Diff for: .codecov.yml

@@ -17,3 +17,6 @@ ignore:
   - "google/cloud/iam"
   - "google/cloud/logging"
   - "google/cloud/spanner/admin"
+  - "google/cloud/pubsublite"
+  - "google/cloud/secretmanager"
+  - "google/cloud/tasks"

Diff for: ci/cloudbuild/builds/cmake-install.sh

@@ -170,7 +170,7 @@ done
 
 # Tests the installed artifacts by building and running the quickstarts.
 # shellcheck disable=SC2046
-libraries="$(printf ";%s" $(quickstart::libraries))"
+libraries="$(printf ";%s" $(features::list | grep -v experimental-))"
 libraries="${libraries:1}"
 cmake -G Ninja \
   -S "${PROJECT_ROOT}/ci/verify_quickstart" \