Port postgres to Go and install the extensions a consumer asks for

letta crash-loops on 'type "vector" does not exist': pgvector is not a
trusted extension, so only the provider's superuser can create it, and
the provisioner never did. A contribution may now name extensions; the
provider creates each (IF NOT EXISTS, available ones only) in the
consumer's database on every pass. Go per the standing rule for a
TypeScript module that changes. letta asks for vector.

modules/letta/module.json

@@ -10,7 +10,10 @@
   ],
   "contributes": {
     "postgres-database": {
-      "name": "letta"
+      "name": "letta",
+      "extensions": [
+        "vector"
+      ]
     },
     "route": {
       "label": "letta",