Description field for media styles

Problem/Motivation

Media styles and responsive image styles can have a name, but often over time it becomes unclear where what style is used.
As a result site builders and frontend developers start adding more and more media styles because changing an existing one might break things...

Proposed resolution

Add a description field that is visible on the admin pages, where information about the use of that style can be given and updated over time.

Remaining tasks

User interface changes

This is a change in the admin interface.

API changes

Data model changes

Release notes snippet