[docs] Update s3.region in quickstart docs of flink and lakehouse

### Search before asking

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

### Fluss version

0.9.0 (latest release)

### Please describe the bug 🐞

### Solution

* default: RUSTFS_REGION="us-east-1"
* add: s3.region: us-east-1

### Are you willing to submit a PR?

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

Inspect the quickstart documentation for Flink and lakehouse, locating the current RUSTFS_REGION and S3 configuration examples. Update the examples to include s3.region: us-east-1, and verify that both quickstarts consistently show the requested setting.

Written by the indexing model from the issue text.