Unable to delete segments - 504 Gateway Timeout

### How are you running Flagsmith

- [x] Self Hosted with Docker
- [ ] Self Hosted with Kubernetes
- [ ] SaaS at flagsmith.com
- [ ] Some other way (add details in description below)

### Describe the bug

DELETE request to segments fail with timeout error and not actually removed.
We have ~4 800 000 identities and various segments.
Once segment becomes obsolete, we are unable to remove it.
Any attempt fail with timeout.

When removing through django admin, I receive 400 Bad Request error.
Is there any way to cleanup unused segments? maybe with postgres DB?
Just want to make sure that unused segments no longer served and won't take any DB disk

### Steps To Reproduce

1. Go to segments
2. Delete any segment
3. Wait until timeout
4. Reload the page
5. Observe that segment is still present

### Expected behavior

1. Go to segments
2. Delete any segment
3. Wait until segment is removed
4. Reload the page
5. Observe that segment is gone

### Screenshots

_No response_