nginx: support certificates for multiple domains

Uses `tls_domains` config context property from NetBox.

roles/nginx/README.md

@@ -0,0 +1,3 @@
+Install nginx, set up generic HTTPS redirects and the .well-known directory.
+
+Acquire Let’s Encrypt certificates for the primary IP `dns_name` and any domains listed in the `tls_domains` context property.

roles/nginx/tasks/main.yml

@@ -26,7 +26,11 @@
 
 - name: Get LE certificate
   command:
-    cmd: certbot certonly --non-interactive --agree-tos --register-unsafely-without-email --webroot --webroot-path /srv/http -d {{ dns_name }}
+    cmd: >
+      certbot certonly
+          --non-interactive --agree-tos --register-unsafely-without-email
+          --webroot --webroot-path /srv/http
+          -d {{ ([dns_name] + tls_domains|default([])) | join(',') }}
     creates: '/etc/letsencrypt/renewal/{{ dns_name }}.conf'
 
 - name: Install certificate renewal deployment hook