Add proper templating with vault keys

Rather than copying a template to the k3os server and editing it in vim,
us yq to generate a template with values stored in vault (token and
server_url). Update the README to reflect these changes.

.gitignore

@@ -1,4 +1,5 @@
 server/
+templates/
 *.crt
 *.pem
-*.key
+*.key