Add script keyword link in tooltip

What does this MR do and why?

Adds the markdown description to the JSON schema for the script keyword as it was forgotten in the previous MR. Note that the "dark blobs" in the screenshot is a different issue with the dark theme code edtiors and is unrelated to this issue.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Go to the pipeline editor
2. Add a job with the script keyword. Something like:

my_job:
  script: echo hello

3. Hover on the script keyword
4. Notice that you now see the Learn more link
5. Click on it
6. It takes you to the script keyword in our docs

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.