roles/nginx: Switch to acme.sh for Let's Encrypt

The certbot-auto client that I've been using for a long time is now
only supported if you install it using snap. I don't use snap on my
systems so I decided to switch to the acme.sh client, which is imp-
lemented in POSIX shell with no dependencies. One bonus of this is
that I can start using ECC certificates.

This also configures the .well-known directory so we can use webroot
when installing and renewing certificates. I have yet to understand
how the renewal works with regards to webroot, though. I may have to
update the systemd timers to point to /var/lib/letsencrypt/.well-known.

roles/nginx/templates/vhost.conf.j2

@@ -14,6 +14,8 @@ server {
     listen [::]:80;
     server_name {{ domain_name }} {{ domain_aliases }};
 
+    {% include 'well-known.j2' %}
+
     # redirect http -> https
     location / {
         # ? in rewrite makes sure nginx doesn't append query string again