Requests should stay within Docker Network

I have a single machine deployment.

It looks like the `lk-jwt-service` tries to reach `synapse` via host instead of internal docker network dns.
When ufw is enabled and blocking everything that is not allowed, livekit calls do not work.

The ufw logs are like:\
`[UFW BLOCK] IN=br-...... SRC=172.18.0.2 DST=192.168.0.2 PROTO=TCP DPT=443`

The lk-jwt-service logs are like:\
`Failed to look up user info: Get matrix://matrix.myserver.com/_matrix/......`

What i would have expected is:\
`matrix://synpase-server:8008`

```compose
services:
lk-jwt:
image: ghcr.io/element-hq/lk-jwt-service:latest
environment:
LIVEKIT_JWT_BIND: ":8080"
LIVEKIT_URL: "ws://livekit:7880"
LIVEKIT_KEY: mykey
LIVEKIT_SECRET: mysecret
LIVEKIT_FULL_ACCESS_HOMESERVERS: "synapse:8008"
networks:
- synapse-net
```