Add docstring to LiteLLM embedding class

[fadil4u]

Description

Add a docstring for LiteLLMEmbedding class to provide complete documentation for the class and its arguments.
This class previously had no docstring, so there was no docs for LiteLLM embedding.

Fixes # (no issue)

New Package?

• Yes
• No

Version Bump?

• Yes
• No

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• I added new unit tests to cover this change
• Not applicable — docstring-only change

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