rc: bring back the early installer as optional importer

This sort of reverts commit 5f319ade.

src/etc/rc.bootup

@@ -65,6 +65,26 @@ echo "done.\n";
  */
 system_console_mute();
 
+/* loopback device is required early for syslog and the installer */
+interfaces_loopback_configure(true);
+
+$setup_installer = is_install_media();
+if ($setup_installer) {
+    echo 'Press any key to start the configuration importer:  ';
+
+    $key = timeout();
+    if ($key != "\n") {
+        echo "\n";
+    }
+
+    if (isset($key)) {
+        passthru('/usr/local/etc/rc.importer');
+    }
+
+    /* config may have changed via installer import */
+    OPNsense\Core\Config::getInstance()->forceReload();
+}
+
 global $config;
 $config = parse_config(true);
 convert_config();
@@ -138,7 +158,7 @@ if ($ipsec_dynamic_hosts) {
 // generate configuration data for all installed templates
 configd_run('template reload *');
 
-if (is_install_media()) {
+if ($setup_installer) {
     /*
      * Installer mode requires setting up an extra user and
      * we will protect it with root's password.  We can only

src/etc/rc.installer

@@ -79,4 +79,4 @@ for n in 5 4 3 2 1; do
 done
 echo
 
-/usr/local/etc/rc.reboot
+reboot