feat: Add examples/templates/do-linux for Digital Ocean Droplets

[mafredri]

This PR adds an example that provisions workspaces as Digital Ocean Droplets and mounts a persistent volume for the users (coder) home directory.

I wanted to provision the workspaces in a specified Digital Ocean Project, but due to terraform detecting this as two workspace volumes, there's a side-effect of not being able to SSH into the workspace.

For now, the project specification is commented out:

# resource "digitalocean_project_resources" "project" {
#   project = var.step2_do_project_id
#   # Workaround for terraform plan when using count.
#   resources = length(digitalocean_droplet.workspace) > 0 ? [
#     digitalocean_volume.home_volume.urn,
#     digitalocean_droplet.workspace[0].urn
#     ] : [
#     digitalocean_volume.home_volume.urn
#   ]
# }

See #1750 for details on the issue.

[kylecarbs]

We could even make the username their Coder username 👀

[mafredri]

Oh I love that!

[coadler]

Super small nit, but do-droplet seems slightly redundant. For the other clouds we have gcp-linux, aws-linux, etc instead of gcp-gce-linux and aws-ec2-linux.

[mafredri]

@coadler My motivation for using droplet was that DO offers managed k8s as well, and if we'd want to have one for that as well, what would we call it? I'm OK with making the change though.

[coadler]

This is true for the other clouds too though. Maybe we should have subfolders for each cloud? Don't mean to derail this at all, just thinking out loud!

[mafredri]

Good point. How about I make the change here to standard naming scheme, then we can consolidate later? At the risk of bike-shedding, I do kind of like that the name explains exactly what it is since the name is often inherited from the folder name. So we'd have gcp-gce-linux instead of gce-linux (via gcp/gce-linux).

[coadler]

Works for me!

[mafredri]

I wanted to conditionally include Fedora images based on if SSH key is set, but it's not possible, unfortunately :/ hashicorp/terraform#25609

[johnstcn]

Looking great!

[mafredri]

Right now we leave the SSH server running on the Droplet. I think this is OK, if someone doesn't want that, they can edit the cloud-config to disable it. Or should it be an option?

With the last commit (08483d8) we could in theory use remote-exec instead of cloud-config (when SSH key is provided). But perhaps that could be left for an alternative implementation of this template.