Draft: Added information popover support to widget extensions

What does this MR do and why?

Adds support for an information popover in merge request widget extensions. To add a popover - just add an additional property the extension definition:

popover: {
    title: 'Title goes here',
    content: 'Content goes here. Include HTML if needed',
},

Screenshots or screen recordings

How to set up and validate locally

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.

#341048 (closed)