Update default bot comment text when approvals required

What does this MR do and why?

Improve bot comment description to help customers better understand common reasons why approval is required by security policies for a given MR, without leaving the MR.

Closes #439503 (closed).

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

In order to display the bulleted list, the table had to be removed:

Required approvals	Optional approvals

How to set up and validate locally

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