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/renew-letsencrypt.service.j2

@@ -1,7 +1,9 @@
 [Unit]
 Description=Renew Let's Encrypt certificates
-ConditionFileIsExecutable={{ letsencrypt_certbot_dest }}
+ConditionFileIsExecutable={{ letsencrypt_acme_home }}/acme.sh
 
 [Service]
 Type=oneshot
-ExecStart={{ letsencrypt_certbot_dest }} renew --standalone --pre-hook "/bin/systemctl stop nginx" --post-hook "/bin/systemctl start nginx"
+ExecStart={{ letsencrypt_acme_home }}/acme.sh --cron --home {{ letsencrypt_acme_home }} --reloadcmd "/bin/systemctl reload nginx"
+
+SuccessExitStatus=0 2