[Feature] [SWCK] Add doc for BanyanDB CRD and Controller

### Search before asking

- [X] I had searched in the [issues](https://github.com/apache/skywalking/issues?q=is%3Aissue) and found no similar feature requirement.

### Description

As we already have the [BanyanDB CRD and Controller](https://github.com/apache/skywalking-swck/pull/70), but there are no docs on how to use it.

### Use case

_No response_

### Related issues

_No response_

### Are you willing to submit a PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)