nginx timeout when exporting large project via POST /api/projects/{project_id}/exports

**Describe the bug**
We experienced nginx timeout errors when using the [recommended export snapshot API](https://labelstud.io/api#tag/Export/operation/api_projects_exports_create) to export a large project.

The `POST /api/projects/{project_id}/exports` API succeeded for this large project prior to the 1.12.0 update.

The project has ~18000 tasks, ~25000 annotations, and each task has ~2kb of data. The size of the project's JSON export is ~110MB.

The nginx timeout errors have the following form:
```
2024/05/02 13:22:03 [warn] 21#21: *173314 upstream server temporarily disabled while reading response header from upstream, client: 10.128.xxx.xxx, server: , request: "POST /api/projects/14/exports HTTP/1.1", upstream: "http://127.0.0.1:8000/api/projects/14/exports", host: ""
2024/05/02 13:22:03 [error] 21#21: *173314 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 10.128.xxx.xxx, server: , request: "POST /api/projects/14/exports HTTP/1.1", upstream: "http://127.0.0.1:8000/api/projects/14/exports", host: ""
```

**To Reproduce**
Steps to reproduce the behavior:
1. Create a large project with 18000 tasks, 25000 annotations, and ~2kb of data per task.
2. `POST /api/projects/{project_id}/exports`
3. Observe nginx timeout errors

**Expected behavior**
`POST /api/projects/{project_id}/exports` succeeds regardless of the size of the project size.

**Environment (please complete the following information):**
- Label Studio version 1.12.0