Aws bedrock reranker

[yashikabadaya]

Description

Added AWS Bedrock as a reranker provider in the docs:

• Example configuration for AWS Bedrock reranker is now included.
• AWS Bedrock is listed among supported reranker models.

Added code changes to support AWS Bedrock reranker.

Fixes #3501

Type of change

Please delete options that are not relevant.

New feature (non-breaking change which adds functionality) Documentation update

How Has This Been Tested?

• [ ] Unit Test
• make build ensures code builds properly.

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules
• [x] I have checked my code and corrected any misspellings

Maintainer Checklist

• [ ] closes #3501
• [ ] Made sure Checks passed