[docs] Lance Quickstart documentation with vector search example

### Search before asking

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

### Motivation

Lance Quickstart documentation (similar to existing Paimon and Iceberg) but with vector search example.

### Solution

_No response_

### Anything else?

_No response_

### Willingness to contribute

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

Start by comparing the existing Paimon and Iceberg quickstart documentation. Add an equivalent Lance quickstart with a vector search example; done means the new documentation covers the requested workflow clearly.

Written by the indexing model from the issue text.