Update Wiki content as needed for new cluster setup

[geerlingguy]

• Change mentions of 5 or 6 nodes to 4 Pis default, with the ability to easily (well, sorta) scale to 200+ Pis.
• Change any mentions of the full cluster specs (in README and elsewhere) to adapt it to 4 Pis as the baseline.
• Create a new Kubernetes-centric architecture diagram for the following Wiki page: http://www.pidramble.com/wiki/setup/provision
• Update pages which still describe the old cluster setup/architecture to use the new process (and move any redundant info out of the Pi Dramble project README).
  • Provision the Raspberry Pis
  • Deploy Drupal to the Raspberry Pis

[geerlingguy]

Almost done here... I have all the Wiki pages updated until the 'Deploy Drupal to the Raspberry Pis' page. And in fact, the new way the cluster works, you technically don't need to 'Deploy Drupal' anymore. But I'll have to figure out how I want to rework that page (and redirect the URL if I change it!) soon enough. Getting a bit tired for the evening, and I still need to work more on the 2019 edition slides for a few presentations I'm giving over the next 30 days!

[geerlingguy]

Annnnd, done!