throw exception in `BaseBrokerStarter#getDefaultBrokerId()`

`brokerId` is assigned as below:([code](https://github.com/apache/pinot/blob/24c5d8fe8521b91e68dd07294a3f57b067c0d525/pinot-broker/src/main/java/org/apache/pinot/broker/broker/helix/BaseBrokerStarter.java#L280))
```
String brokerId = _brokerConf.getProperty(Broker.CONFIG_OF_BROKER_ID, getDefaultBrokerId());
```

A valid value for `brokerId` is important in many components, for example it's required in v2 engine to guarantee an unique requestId. It's preferred to throw an exception to stop broker starter instead of return an empty string.
```
private String getDefaultBrokerId() {
try {
return InetAddress.getLocalHost().getHostName();
} catch (Exception e) {
LOGGER.error("Caught exception while getting default broker Id", e);
return "";
}
}
```

cc @jackjlli

Read the linked BaseBrokerStarter.java location and inspect getDefaultBrokerId() together with the brokerId assignment. Verify the broker startup behavior when InetAddress.getLocalHost().getHostName() fails, and confirm that a valid configured broker ID remains unaffected. Done means startup no longer proceeds with an empty default broker ID.

Written by the indexing model from the issue text.