Opensearch similarity search should include index name

[quachc]

Bug description
SearchRequest does not include index name which results in an error when using Opensearch role own_index:
no permissions for [indices:data/read/search] and User [name=...]

Environment
Spring AI 1.0.0-SNAPSHOT
Java 21,
Opensearch 2.14.0

Steps to reproduce
Create an user with permissions for a single index (e.g. role own_index)

Expected behavior
Should be able to execute the similarity search without errors

Minimal Complete Reproducible example
Not available...

[inpink]

I have addressed this issue in the submitted PR #1435. I kindly request your review of the changes. Thank you! 😊