Draft: Add generate description button to New issue page

What does this MR do and why?

Most FE moved to !122882 (closed)

Add description generator to New issue page - https://gitlab.com/gitlab-org/gitlab/-/issues/406791

Remove selecting Template in the prompt, instead just beef up the text a bit. Context in https://gitlab.com/gitlab-org/gitlab/-/issues/406791/#note_1388521079

Screenshots or screen recordings

Screen_Recording_2023-05-18_at_20.47.13

How to set up and validate locally

1. In rails console enable the experiment fully

   Feature.enable(:openai_experimentation)
   Feature.enable(:generate_description_ai)

2. In a public project, create a new issue

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.