disable template creation by pubsubbeat

The default pubsubbeat configuration is to create templates for indices: https://github.com/GoogleCloudPlatform/pubsubbeat/blob/master/pubsubbeat.reference.yml#L722

However, we want to have more control over the template creation process so instead we're using the API for this. Until now, there were two templates created that were conflicting. This change disables template creation by pubsubbeat.

For more context see: https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/7887#note_218869109