Troubleshooting Guide

### Search before asking

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

### Description

Create a troubleshooting guide for Lakehouse that can contain examples of lib vs plugins directory usage or Common dependency error scenarios (if one doesn't exist)

### Willingness to contribute

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

Start by reviewing the existing Lakehouse documentation and locating the lib and plugins directories mentioned in the issue. Identify common dependency-error scenarios, then document the directory-usage examples and troubleshooting steps in a clearly discoverable guide.

Written by the indexing model from the issue text.