terminal-util: tweak any_key_to_proceed() a bit

1. Make the message a bit more visible, by adding ANSI color. This
   matters in particular during boot, where the message otherwise might
   be overprinted by other output

2. Let's turn off terminal echo so that whatever key is entered is not
   made visible on screen, and we can handle newline and other keys
   reasonably uniformly.

src/firstboot/firstboot.c

@@ -128,7 +128,7 @@ static void print_welcome(int rfd) {
         else
                 printf("\nWelcome to your new installation of %s!\n", pn);
 
-        printf("\nPlease configure your system!\n\n");
+        printf("\nPlease configure your system!\n");
 
         any_key_to_proceed();