flatpak: the package, Flathub with it, and the installations as tools (hq to-be 42 phase 2.9)

The package ships Flathub in /usr/share/flatpak/remotes.d, so the module
declares no remote of its own and checks it instead. Eleven Go tools: list,
runtimes, remotes (naming the desktop's duplicate user Flathub), updates,
unused, disk usage, and install, remove, update and remove-unused, the
system installation's acts through sudo -n and the account's without.

uninstall --unused has no dry run, so flatpak_unused works it out from
flatpak's own answers: an application's runtime and SDK, the extension
points of what is used, and pins. Acts run as jobs inside the bundle,
because an install outlasts a call.

modules/flatpak/module.json

@@ -0,0 +1,42 @@
+{
+  "module": "flatpak",
+  "version": "1",
+  "capabilities": [
+    "package-manager"
+  ],
+  "tools": [
+    "flatpak_list",
+    "flatpak_runtimes",
+    "flatpak_remotes",
+    "flatpak_updates",
+    "flatpak_unused",
+    "flatpak_disk_usage",
+    "flatpak_install",
+    "flatpak_remove",
+    "flatpak_update",
+    "flatpak_remove_unused",
+    "flatpak_job"
+  ],
+  "resources": [
+    {
+      "id": "package",
+      "type": "package",
+      "package": "flatpak"
+    }
+  ],
+  "build": {
+    "artifacts": [
+      {
+        "name": "tools",
+        "kind": "bundle",
+        "language": "go",
+        "system": "arch",
+        "from": "cmd/flatpak-tools",
+        "binary": "flatpak-tools",
+        "loads": [
+          "flatpak-tools"
+        ]
+      }
+    ]
+  }
+}