Standardize nginx setup in install scripts

Refactors many install scripts to use the shared `nginx_enable_site` helper instead of manual symlink/default-site/reload sequences, making webserver setup more consistent and less error-prone. It also replaces hardcoded PHP-FPM socket paths with `get_php_fpm_socket` (including templated substitutions where needed) across nginx and caddy configs to improve compatibility with varying PHP versions and socket locations.

install/librenms-install.sh

@@ -80,7 +80,7 @@ sed -i "s/listen = \/run\/php\/php8.4-fpm.sock/listen = \/run\/php-fpm-librenms.
 msg_ok "Configured PHP-FPM"
 
 msg_info "Configure Nginx"
-cat <<EOF >/etc/nginx/sites-enabled/librenms
+cat <<EOF >/etc/nginx/sites-available/librenms
 server {
  listen      80;
  server_name ${LOCAL_IP};
@@ -103,8 +103,7 @@ server {
  }
 }
 EOF
-rm /etc/nginx/sites-enabled/default
-$STD systemctl reload nginx
+nginx_enable_site librenms
 systemctl restart php8.4-fpm
 msg_ok "Configured Nginx"