Containerize the frontend web VM scale set

We'd like to containerize at least the frontend web VM scale set, if not the entire cluster. Kubernetes is considered a viable orchestrator, but it's uncertain how app containers may be deployed using ARM templates, so need investigation on that.

We also learned recently that Catalyst IT EU presented their Moodle containerization experiences in [MoodleMoot UK/Ireland 2018](https://moodlemoot.org/mootieuk18/program/) (search for "containerisation" after clicking the link), and it'd be great if we can learn and improve from their experiences.

Initially setting the milestone as v1.5.1 for planning, but it's well understood that this work might take longer, in which case the milestone will be adjusted accordingly.