Add option to use existing Fabric install to avoid metadata query

[Discussion in Discord](https://discord.com/channels/660567679458869252/660569755320844308/1475145066304770230)

Hi, I have a question about the Minecraft server Docker image.

I have this compose:

```yaml
services:
mc:
image: itzg/minecraft-server:java21-jdk
tty: true
stdin_open: true
restart: always
ports:
- "25565:25565"
environment:
EULA: "TRUE"
TYPE: "FABRIC"
ENABLE_COMMAND_BLOCK: "true"
ENABLE_WHITELIST: "true"
WHITELIST: |-
xx
xxx
VERSION: "1.21.1"
MEMORY: "10240M"
MAX_PLAYERS: "2"
OPS: |-
xx
ALLOW_FLIGHT: "true"
volumes:
- "./data:/data"
```

The server always tries to download Fabric when TYPE=FABRIC. In Spain, sometimes Cloudflare is blocked due to football events (yeah, it sucks). When this happens, meta.fabricmc.net and its IPs are blocked, among other sites.

Is it possible to avoid downloading Fabric every time the server starts?

Start with the Docker Compose configuration in the issue and trace the startup path selected by TYPE=FABRIC, focusing on how the mounted /data volume is handled. Reproduce a restart with the existing Fabric installation while meta.fabricmc.net is unavailable. Done means the server can reuse that installation without querying Fabric metadata each time.

Written by the indexing model from the issue text.