Collapse help into expandable command topics

plugins/domains/commands

@@ -4,7 +4,9 @@ set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
 
 case "$1" in
   help | domains:help)
-    cat<<EOF
+    help_content_func () {
+      declare desc="return help_content string"
+      cat<<help_content
     domains [<app>], List domains
     domains:add <app> DOMAIN, Add a domain to app
     domains:clear <app>, Clear all domains for app
@@ -12,7 +14,19 @@ case "$1" in
     domains:enable <app>, Enable VHOST support
     domains:remove <app> DOMAIN, Remove a domain from app
     domains:set-global <domain>, Set global domain name
-EOF
+help_content
+    }
+
+    if [[ $1 = "domains:help" ]] ; then
+        echo -e 'Usage: dokku domains[:COMMAND]'
+        echo ''
+        echo 'Manage vhost domains used by the Dokku proxy.'
+        echo ''
+        echo 'Additional commands:'
+        help_content_func | sort | column -c2 -t -s,
+    else
+        help_content_func
+    fi
     ;;
 
   *)