feat(webtop): add Ubuntu XFCE web desktop

webtop/.env.example

@@ -0,0 +1,13 @@
+# Copy to .env and fill in. Never commit .env.
+#
+#   cp .env.example .env
+
+# Login for the web desktop, also the abc user's sudo password.
+# Generate one with: openssl rand -base64 24
+CUSTOM_USER=abc
+PASSWORD=
+
+TZ=Asia/Ho_Chi_Minh
+
+# Browser tab title.
+# TITLE=Webtop