Added cert-manager and https cert automatic issuing

[dm3ch]

Add installation of cert-manager

/fix #11

[zaslavskii]

WDYT if we install certmanager using helm provider like it is done here?
https://github.com/chainstack/infrastructure/tree/master/tf-modules/helm/certmanager

I don't want to increase the complexity of the repository by nesting directories. Also the number of manual steps users need to go through is undesirable IMHO.

I understand that you don't want to duplicate certmanager installation in each tf module.

[dm3ch]

WDYT if we install certmanager using helm provider like it is done here?
https://github.com/chainstack/infrastructure/tree/master/tf-modules/helm/certmanager

I don't want to increase the complexity of the repository by nesting directories. Also the number of manual steps users need to go through is undesirable IMHO.

I understand that you don't want to duplicate certmanager installation in each tf module.

I decided not to add that to terraform (at least for now) cause:

1. It could be useful for bare-metal clusters (which are not covered by our terraform)
2. It doesn't depends on any terraform resource outputs.

I also don't like idea adding more nested structures, but I'm going to merge on helmfile in future, so I think it would be simplified in 3rd milestone.

P.S. Also this helmfile is going to contain kube-dashboard and prometheus+grafana installation