Add a namespace to the click handler registration for `.insert-media` in `media-editor.js`: `click.add-media-button`.

This is a stopgap to allow devs to override the default behavior.

Fixes #23096.


git-svn-id: https://develop.svn.wordpress.org/trunk@29802 602fd350-edb4-49c9-b593-d223f7449a82