add NUT Server to the catalog

- NUT Server (instantlinux/nut-upsd) runs the Network UPS Tools server for a UPS connected to the host by USB: the installation proposes the UPS the host detects, passes it to the container, generates the password of the upsmon user and starts with the host; clients such as PeaNUT connect on port 3493.
- A recipe can ask for the UPS of the host: without one, the installation stops and says so, and the advanced installation lets the node be typed by hand.
- The catalog lists 335 applications.
- Tests for the proposed UPS, a host without one and the recipe.

AppImage/messages/en/common.json

@@ -5014,7 +5014,9 @@
   "lxcTerminal": {
     "title": "Terminal: {name} (ID: {id})",
     "errors": {
-      "invalidVmid": "Invalid VMID — refusing to execute pct enter"
+      "invalidVmid": "Invalid VMID — refusing to execute pct enter",
+      "noShell": "This container's image has no shell, so it cannot open a terminal. Its output is in the Logs tab.",
+      "enterFailed": "The container could not be entered."
     },
     "commands": {
       "listFiles": "List all files with details",