[bug]: Cannot use service name as webhook URL

Is there an existing issue for this?

• I have searched the existing issues

Current behavior

When entering a webhook URL, I'd like to be able to use services I add to the docker compose file as part of the URL. For example, this is supported for the email SMTP server URL (it's currently set to emailproxy and port 2465 so I can use OAuth for emails)
I have a container that will forward webhooks to Discord, and I would like to be able to use this URL:
http://plane-discord-webhook-bridge:8000/webhook

However, I get a 400 response in in the API logs as well as the browser console when entering this URL.

The workaround for this is exposing it to the internet or using a local IP address such as 192.168.1.123:8000 instead.

Steps to reproduce

1. Create another service in the docker-compose file generated in the plane-selfhost/plane-app directory and restart the stack
2. Go into Workspace Settings
3. Go into Webhooks
4. Enter the URL referring to the service such as http://plane-discord-webhook-bridge:8000/webhook
5. Attempt to create the webhook and observe error in API logs (from setup.sh) and browser console.

Environment

Production

Browser

None

Variant

Self-hosted

Version

v0.27.1