Document feature_spaces_metaspaces (#19679)

Co-authored-by: Jonathan de Jong <jonathandejong02@gmail.com>

docs/labs.md

@@ -149,3 +149,8 @@ Maximised widgets provide a room layout in which a widget is (temporarily) the p
 
 Note that this feature is currently under active development and therefore is
 entirely incomplete and may not work at all - it is not recommended for general use at this time.
+
+## Metaspaces (`feature_spaces_metaspaces`) [In Development]
+
+Metaspaces are automatically populated spaces you can enable in your Space panel.
+By default, you'll have Home or All rooms, but you can opt in to a People, Favourites, and Other Rooms metaspace too.

element.io/develop/config.json

@@ -56,5 +56,8 @@
     "posthog": {
         "projectApiKey": "phc_Jzsm6DTm6V2705zeU5dcNvQDlonOR68XvX2sh1sEOHO",
         "apiHost": "https://posthog.hss.element.io"
+    },
+    "features": {
+        "feature_spaces_metaspaces": true
     }
 }