Include observability quickstart files in binary distribution

### Search before asking

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

### Motivation

Currently, the configuration files of the observability quickstart guide are packages as a zip file, which is not version control-friendly. The files should be included in the binary distribution of fluss.

### Solution

- Include the logback configuration file in `conf/`.
- Include configuration files of third party applications (e.g., Prometheus) in `examples/quickstart-observability/`
- Adapt the observability quickstart guide

### Anything else?

_No response_

### Willingness to contribute

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

Start by locating the binary distribution packaging and the observability quickstart guide. Review the existing zip-based configuration files, then place the logback file under conf/ and third-party application files under examples/quickstart-observability/. Done means the binary distribution contains these files and the quickstart guide matches their new locations.

Written by the indexing model from the issue text.