FIX Allow wrapping an image in a link

[GuySartorelli]

A TinyMCE 6 compliant version of https://github.com/silverstripe/silverstripe-asset-admin/pull/1397

Also migrates some behat fixture logic to the behat-extension module, so that it can be used by other modules for their related behat tests.

Make sure you check the installer CI run linked in the issue to see behat passing happily

Requires

• https://github.com/silverstripe/silverstripe-admin/pull/1579
• https://github.com/silverstripe/silverstripe-behat-extension/pull/249

Issue

• https://github.com/silverstripe/silverstripe-admin/issues/1548