Hotfix: correctly handle custom parameters

What does this merge request do and why?

Correctly handle custom parameters for code-suggestions models by merging it with default parameters

Context https://gitlab.slack.com/archives/C06DCB3N96F/p1717771611615999

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Merge request checklist

• I've ran the affected pipeline(s) to validate that nothing is broken.
• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.