[TOOLS][DOCKER] Rewrite the configuration script to use whiptail/dialog, and refactor

docker/certbot/docker-compose.fragment.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/sh
+
+cat <<EOF
+    certbot:
+        image: certbot/certbot
+EOF
+
+# If the user wants a nginx docker container
+if echo "${DOCKER}" | grep -Fvq '"nginx"'; then
+    cat <<EOF
+        depends_on:
+            - nginx
+EOF
+fi
+cat <<EOF
+        # Check for certificate renewal every 12h as
+        # recommended by Let's Encrypt
+        entrypoint: /bin/sh -c 'trap exit TERM;
+                                while :; do
+                                    certbot renew > /dev/null;
+                                    sleep 12h & wait \$\${!};
+                                done'
+        volumes:
+          - ./docker/certbot/www:/var/www/certbot
+          - ./docker/certbot/.files:/etc/letsencrypt
+
+EOF