[sam2][demo][1/x] Fix file upload

Summary:

The Strawberry GraphQL library recently disabled multipart requests by default. This resulted in a video upload request returning "Unsupported content type" instead of uploading the video, processing it, and returning the video path.

This issue was raised in #361. A forward fix is to add `multipart_uploads_enabled=True` to the endpoint view.

Test Plan:

Tested locally with cURL and upload succeeds

*Request*

```
curl http://localhost:7263/graphql \
  -F operations='{ "query": "mutation($file: Upload!){ uploadVideo(file: $file) { path } }", "variables": { "file": null } }' \
  -F map='{ "file": ["variables.file"] }' \
  -F file=@video.mov
```

*Response*

```
{"data": {"uploadVideo": {"path": "uploads/<HASH>.mp4"}}}
```