Push Files to Index from Emacs, Obsidian & Desktop Clients using Multi-Part Forms (#499)

### Overview
- Add ability to push data to index from the Emacs, Obsidian client
- Switch to standard mechanism of syncing files via HTTP multi-part/form. Previously we were streaming the data as JSON
  - Benefits of new mechanism
    - No manual parsing of files to send or receive on clients or server is required as most have in-built mechanisms to send multi-part/form requests
    - The whole response is not required to be kept in memory to parse content as JSON. As individual files arrive they're automatically pushed to disk to conserve memory if required
    - Binary files don't need to be encoded on client and decoded on server

### Code Details
### Major
- Use multi-part form to receive files to index on server
- Use multi-part form to send files to index on desktop client
- Send files to index on server from the khoj.el emacs client
  - Send content for indexing on server at a regular interval from khoj.el
- Send files to index on server from the khoj obsidian client
- Update tests to test multi-part/form method of pushing files to index

#### Minor
- Put indexer API endpoint under /api path segment
- Explicitly make GET request to /config/data from khoj.el:khoj-server-configure method
- Improve emoji, message on content index updated via logger
- Don't call khoj server on khoj.el load, only once khoj invoked explicitly by user
- Improve indexing of binary files
  - Let fs_syncer pass PDF files directly as binary before indexing
  - Use encoding of each file set in indexer request to read file 
- Add CORS policy to khoj server. Allow requests from khoj apps, obsidian & localhost
- Update indexer API endpoint URL to` index/update` from `indexer/batch`

Resolves #471 #243

pyproject.toml

@@ -40,6 +40,7 @@ dependencies = [
     "dateparser >= 1.1.1",
     "defusedxml == 0.7.1",
     "fastapi == 0.77.1",
+    "python-multipart >= 0.0.5",
     "jinja2 == 3.1.2",
     "openai >= 0.27.0, < 1.0.0",
     "tiktoken >= 0.3.2",