security.sasl.plain.jaas.config may become incompatible if the Fluss package changes.

### Search before asking

- [x] I searched in the [issues](https://github.com/alibaba/fluss/issues) and found nothing similar.

### Motivation

Currently, we have to config `security.sasl.plain.jaas.config = `com.alibaba.fluss.security.auth.sasl.plain.PlainLoginModule required user_admin="admin-pass" user_developer="developer-pass" user_consumer="consumer-pass"`
This will have two problem:
1. If package name of PlainLoginModule changes, the configuration will be incompatible. For example, because fluss will be repackage to org.apache, user's old config will be incompatible. I don't want to this happens again later.
2. Such as https://github.com/apache/fluss/issues/1071 , we can provide a more friendly configuration to help user generate security.sasl.plain.jaas.config .

### Solution

_No response_

### Anything else?

_No response_

### Willingness to contribute

- [ ] I'm willing to submit a PR!

Start by tracing the PlainLoginModule referenced by security.sasl.plain.jaas.config and reviewing how the Fluss package name is exposed to users. Compare the current JAAS configuration with the requested friendlier configuration, then define tests that verify compatibility when the package changes and that the generated setting is usable.

Written by the indexing model from the issue text.