deployments: have `cert-manager` in code

[cirocosta]

From what I can tell, there's no place in this repo where we deploy the cert-manager crd and the other necessary k8s objects - we're just storing the request for and use of certs.

It'd be great to be able to have all of that here so that we can get the infrastructure up/down & upgraded anytime :grin:

https://hub.helm.sh/charts/jetstack/cert-manager