Support online search with Searxng as turnkey, self-hostable solution

This allows online search to work out of the box again for
self-hosting users, as no auth/api key setup required.

Docker users do not need to change anything in their setup flow.
Direct installers can setup searxng locally or use public instances if
they do not want to use any of the other providers (like Jina, Serper)

Resolves #749. Resolves #990

docker-compose.yml

@@ -18,6 +18,15 @@ services:
     image: ghcr.io/khoj-ai/terrarium:latest
     ports:
       - "8080:8080"
+  search:
+    image: docker.io/searxng/searxng:latest
+    ports:
+      - "42113:8080"
+    volumes:
+      - khoj_search:/etc/searxng
+    environment:
+      - SEARXNG_BASE_URL=http://localhost:42113/
+      - SEARXNG_SECRET_KEY=change_me_to_something_random  # Change this in production
   server:
     depends_on:
       database:
@@ -51,6 +60,8 @@ services:
       - KHOJ_ADMIN_PASSWORD=password
       # Default URL of Terrarium, the Python sandbox used by Khoj to run code. Its container is specified above
       - KHOJ_TERRARIUM_URL=http://host.docker.internal:8080
+      # Default URL of SearxNG, the default web search engine used by Khoj. Its container is specified above
+      - KHOJ_SEARXNG_URL=http://host.docker.internal:42113
       # Uncomment line below to use with Ollama running on your local machine at localhost:11434.
       # Change URL to use with other OpenAI API compatible providers like VLLM, LMStudio etc.
       # - OPENAI_API_BASE=http://host.docker.internal:11434/v1/
@@ -93,3 +104,4 @@ volumes:
   khoj_config:
   khoj_db:
   khoj_models:
+  khoj_search: