[DOC] Support binary format vector in k-NN

[junqiu-lei]

What do you want to do?
Since OpenSearch 2.16, k-NN plugin introduced binary format vector support, we need update doc for this feature support.

• Request a change to existing documentation
• Add new documentation
• Report a technical problem with the documentation
• Other

Tell us about your request. Provide a summary of the request.
Add doc for this new feature

*Version: List the OpenSearch version to which this issue applies, e.g. 2.14, 2.12--2.14, or all.
Since 2.16

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.
RFC: opensearch-project/k-NN#1767
Task meta: opensearch-project/k-NN#1764