Spring-ai Add documentation for Elasticsearch VectorStore.

Closes #476

Comment From: tzolov

Thank you @Vrryou ,

Hey @eddumelendez , as you contributed the auto-config perhaps you can review the docs as well? I have the feeling that we should use the Boot ES auto-config and related properties in the docs.

Comment From: tzolov

Thank you @Vrryou and @eddumelendez