added cvat_worker_chunk service in docker-compose.external_db.yml (…

…#8871)

### Motivation and context
There was an oversight in the `docker-compose.external_db.yml` file
where the newly added service, `cvat_worker_chunks`, was not configured
to extend the external database environment variables. This resulted in
the `cvat_worker_chunks` container failing to start properly, as it was
stuck in an infinite wait state for a non-existent database connection.

Consequently, jobs failed to open, and attempting to access them
repeatedly caused the Data API to return a 429 status code.

An existing issue related to this problem was reported here:
#8846. However, the author closed
the issue without submitting a pull request to resolve it.

### How has this been tested?

### Checklist
- [x] I submit my changes into the `develop` branch
- [ ] I have created a changelog fragment
- [~] I have updated the documentation accordingly
- [~] I have added tests to cover my changes
- [x] I have linked related issues (see [GitHub docs](

https://help.github.com/en/github/managing-your-work-on-github/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword))
- [ ] I have increased versions of npm packages if it is necessary

([cvat-canvas](https://github.com/cvat-ai/cvat/tree/develop/cvat-canvas#versioning),

[cvat-core](https://github.com/cvat-ai/cvat/tree/develop/cvat-core#versioning),

[cvat-data](https://github.com/cvat-ai/cvat/tree/develop/cvat-data#versioning)
and

[cvat-ui](https://github.com/cvat-ai/cvat/tree/develop/cvat-ui#versioning))

### License

- [x] I submit _my code changes_ under the same [MIT License](
https://github.com/cvat-ai/cvat/blob/develop/LICENSE) that covers the
project.
  Feel free to contact the maintainers if that's a concern.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **New Features**
- Introduced a new service for improved chunk processing in the CVAT
application deployment.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

docker-compose.external_db.yml

@@ -27,6 +27,7 @@ services:
   cvat_worker_import: *backend-settings
   cvat_worker_quality_reports: *backend-settings
   cvat_worker_webhooks: *backend-settings
+  cvat_worker_chunks: *backend-settings
 
 secrets:
   postgres_password: