Increase search distance to get relevant content for chat post indexer update

More content indexed per entry would result in an overall scores
lowering effect. Increase default search distance threshold to counter that

- Details
  - Fix expected results post indexing updates
  - Fix search with max distance post indexing updates

- Minor
  - Remove openai chat actor test for after: operator as it's not expected anymore

src/khoj/routers/api_chat.py

@@ -475,7 +475,7 @@ async def chat(
     common: CommonQueryParams,
     q: str,
     n: Optional[int] = 5,
-    d: Optional[float] = 0.18,
+    d: Optional[float] = 0.22,
     stream: Optional[bool] = False,
     title: Optional[str] = None,
     conversation_id: Optional[int] = None,