Add testing mode that exits on success when server starts fully

Given a timeout and a regex it could:

- exit with failure if java process exits with failure
- exit with failure if timeout expires
- stop the java process and exit with success if the given regex matches a line in stdout

Instead of a log matching regex, it could use rcon to test for server readiness.

Some interesting logs that seem to indicate server is ready:
```
[13:14:17] [Server thread/INFO]: Time elapsed: 22921 ms
[13:14:17] [Server thread/INFO]: Done (58.305s)! For help, type "help"
[13:14:17] [Server thread/INFO]: Starting remote control listener
[13:14:17] [RCON Listener #1/INFO]: RCON running on 0.0.0.0:25575
```

Start by locating the container entry point and how it launches and stops the Java process. Define whether regex-based stdout matching or RCON readiness is the chosen scope, then verify failure on process exit or timeout and success after readiness.

Written by the indexing model from the issue text.