refactor: Add minimal terraform project (#308)

I was thinking it might be nice to have some example projects (especially as we on-board new developers) to make it easy to create new projects.

This adds the most basic possible terraform module... just an output block. However, it's enough to run `coder projects create` and go through the whole lifecycle of creating a project and workspace (although, it's really boring since there are no parameters).

examples/minimal-project/main.tf

@@ -0,0 +1,4 @@
+# The simplest possible Terraform module: it just outputs "Hello, World!"
+output "hello_world" {
+  value = "Hello, World!"
+}