[Feature]: Add mercure.rocks addionnal container

### What is your idea or feature suggestion?

Add support of mercure.rocks in devilbox to add more possibilities for developers with new features

### Benefits

Allow user to make her application more live.

### Where can we find information about this?

[https://mercure.rocks/](https://mercure.rocks/)

# docker-compose.yml
```
version: "3.7"

services:
caddy:
image: dunglas/mercure
restart: unless-stopped
environment:
# Uncomment the following line to disable HTTPS
#SERVER_NAME: ':80'
MERCURE_PUBLISHER_JWT_KEY: '!ChangeMe!'
MERCURE_SUBSCRIBER_JWT_KEY: '!ChangeMe!'
# Uncomment the following line to enable the development mode
#command: /usr/bin/caddy run -config /etc/caddy/Caddyfile.dev
ports:
- "80:80"
- "443:443"
volumes:
- caddy_data:/data
- caddy_config:/config

volumes:
caddy_data:
caddy_config:
```

### Are you willing to provide a PR to address this?

No

Start with the repository's existing container definitions and docker-compose.yml, then review the Mercure documentation linked in the issue. Compare the proposed dunglas/mercure service with the current stack integration; done means Mercure can be enabled alongside Devilbox with its configuration, ports, volumes, and development-mode options working as documented.

Written by the indexing model from the issue text.