Wire up PDF to jsonl processor to Khoj server layer (API, config)

- Specify PDF content to index via khoj.yml
- Index PDF content on app start, reconfigure
- Expose PDF as a search type via API

docker-compose.yml

@@ -21,6 +21,7 @@ services:
       - ./tests/data/ledger/:/data/ledger/
       - ./tests/data/music/:/data/music/
       - ./tests/data/markdown/:/data/markdown/
+      - ./tests/data/pdf/:/data/pdf/
       # Embeddings and models are populated after the first run
       # You can set these volumes to point to empty directories on host
       - ./tests/data/embeddings/:/data/embeddings/