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.

Built from https://develop.svn.wordpress.org/trunk@29802


git-svn-id: http://core.svn.wordpress.org/trunk@29569 1a063a9b-81f0-0310-95a4-ce76da25c4cd