🔧 fix(assistants): Vision minor fix & Add Docs

[danny-avila]

Summary

• Fix/optimization to prevent unnecessary API call if uploaded files are not valid for vision requests
• Adds documentation custom_config.md

Change Type

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

Checklist

• My code adheres to this project's style guidelines
• I have performed a self-review of my own code
• I have commented in any complex areas of my code
• I have made pertinent documentation changes
• My changes do not introduce new warnings
• I have written tests demonstrating that my changes are effective or that my feature works
• Local unit tests pass with my changes
• Any changes dependent on mine have been merged and published in downstream modules.
• New documents have been locally validated with mkdocs