firstboot: make clear where the full screen console wizards end

The three first boot screens are visually separated from the console
output before them via the "chome" and welcome strings and sufficient
whitespace. But so far they weren't from the output after them. This is
sometimes a big confusing. Let's add a bit of a separator between the
end and what comes next, too.

Just cosmetics, nothing else.

src/sysinstall/sysinstall.c

@@ -1249,6 +1249,15 @@ static int settle_definitions(void) {
         return 0;
 }
 
+static void end_marker(void) {
+
+        if (!arg_welcome)
+                return;
+
+        printf("\n%sExiting first boot settings tool.%s\n\n", ansi_grey(), ansi_normal());
+        fflush(stdout);
+}
+
 static int run(int argc, char *argv[]) {
         int r;
 
@@ -1275,6 +1284,7 @@ static int run(int argc, char *argv[]) {
                         chrome_show("Operating System Installer", /* bottom= */ NULL);
         }
 
+        DEFER_VOID_CALL(end_marker);
         DEFER_VOID_CALL(chrome_hide);
 
         _cleanup_(sd_varlink_flush_close_unrefp) sd_varlink *repart_link = NULL;