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

pyproject.toml

@@ -21,6 +21,7 @@ keywords = [
     "markdown",
     "beancount",
     "images",
+    "pdf",
 ]
 classifiers = [
     "Development Status :: 4 - Beta",