Add option to drilldown props from markdown editor to the form field

What does this MR do and why?

In order to support content editor in comments and other areas of GitLab, the content editor's markdown_field component needs to support all the props that the orginal markdown/field.vue component does. However instead of adding attributes to just pass down to the markdown field component, we can add a single object that can drilldown the props to the field, thereby reducing code redundancy and making the template code easier to read.

In a future iteration, I will also add an MR to drilldown props to the markdown field itself (and not just the textarea).

Screenshots or screen recordings

No visible change.

How to set up and validate locally

N/A

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.