Fix doc links / setup (#13140)

* fix various doc links

* update generated start page

* switch to properdocs

* bump deps

* pin mkdocs before 2.0 so deps dont break

* fix link

.devcontainer/devcontainer.json

@@ -53,7 +53,7 @@
       "label": "InvenTree Server"
     },
     "8080": {
-      "label": "mkdocs server"
+      "label": "properdocs server"
     }
   },