fix: add cross_encoder_kwargs parameter for advanced configuration

[hrnayak66]

Description

This PR introduces a new cross_encoder_kwargs parameter to the SentenceTransformerRerank class. This allows users to pass additional configuration options directly to the underlying sentence_transformers.CrossEncoder model, providing greater flexibility for advanced use cases where need to change parameter like local_files_only, cache_dir etc

Fixes #18476

New Package?

Did I fill in the tool.llamahub section in the pyproject.toml and provide a detailed README.md for my new integration or package?

• Yes
• No

Version Bump?

Did I bump the version in the pyproject.toml file of the package I am updating? (Except for the llama-index-core package)

• Yes
• No

Type of Change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• I added new unit tests to cover this change
• I believe this change is already covered by existing unit tests

Suggested Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added Google Colab support for the newly added notebooks.
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I ran uv run make format; uv run make lint to appease the lint gods