Add support per user for configuring the preferred search model from the config page

- Honor this setting across the relevant places where embeddings are used
- Convert the VectorField object to have None for dimensions in order to make the search model easily configurable

src/khoj/routers/api.py

@@ -332,6 +332,31 @@ async def update_chat_model(
     return {"status": "ok"}
 
 
+@api.post("/config/data/search/model", status_code=200)
+@requires(["authenticated"])
+async def update_chat_model(
+    request: Request,
+    id: str,
+    client: Optional[str] = None,
+):
+    user = request.user.object
+
+    new_config = await adapters.aset_user_search_model(user, int(id))
+
+    update_telemetry_state(
+        request=request,
+        telemetry_type="api",
+        api="set_search_model",
+        client=client,
+        metadata={"search_model": new_config.setting.name},
+    )
+
+    if new_config is None:
+        return {"status": "error", "message": "Model not found"}
+
+    return {"status": "ok"}
+
+
 # Create Routes
 @api.get("/config/data/default")
 def get_default_config_data():
@@ -410,14 +435,10 @@ async def search(
         defiltered_query = filter.defilter(defiltered_query)
 
     encoded_asymmetric_query = None
-    if t == SearchType.All or t != SearchType.Image:
-        text_search_models: List[TextSearchModel] = [
-            model for model in state.search_models.__dict__.values() if isinstance(model, TextSearchModel)
-        ]
-        if text_search_models:
-            with timer("Encoding query took", logger=logger):
-                search_model = await sync_to_async(get_user_search_model_or_default)(user)
-                encoded_asymmetric_query = state.embeddings_model[search_model.name].embed_query(defiltered_query)
+    if t != SearchType.Image:
+        with timer("Encoding query took", logger=logger):
+            search_model = await sync_to_async(get_user_search_model_or_default)(user)
+            encoded_asymmetric_query = state.embeddings_model[search_model.name].embed_query(defiltered_query)
 
     with concurrent.futures.ThreadPoolExecutor() as executor:
         if t in [
@@ -473,9 +494,9 @@ async def search(
                     results += text_search.collate_results(hits, dedupe=dedupe)
 
                 # Sort results across all content types and take top results
-                results = text_search.rerank_and_sort_results(results, query=defiltered_query, rank_results=r)[
-                    :results_count
-                ]
+                results = text_search.rerank_and_sort_results(
+                    results, query=defiltered_query, rank_results=r, search_model_name=search_model.name
+                )[:results_count]
 
     # Cache results
     if user: