Changes prompt in ai_genie to work with text as well

What does this MR do and why?

Changes prompt in ai_genie to work with text as well

Screenshots or screen recordings

code	not code

How to set up and validate locally

1. Enable the following feature flags:
   • explain_code
   • explain_code_snippet
   • openai_experimentation
   • ai_experimentation_api
2. Add an OpenAI API key by following the steps in !116364 (merged)
3. Run the following command in the root of your project:
   • curl https://gitlab.com/gitlab-org/gitlab/-/merge_requests/117636.diff | git apply
   • This will apply changes from !117636 (merged) on which this MR relies.
4. Open a file containing Source Code (Note, this file should not be from the GitLab codebase).
   • sample_file.js
5. Highlight some of the Source Code.
6. Click on the (?) button in the gutter to the left of the source code.
7. Try same in markdown and Jupyter rendered code/no code

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #409980