Create a route for bulk deleting all Kontainer media

Problem/Motivation

Currently, a user cannot filter for all Kontainer media types at once on the Media Overview page. Deleting all of the Kontainer media is also a requirement for deleting the module. A link should be added to the system uninstall form, which has a link for deleting all the media (see the file module for example).

Proposed resolution

Alter/add an uninstall content validation and add a link leading to an endpoint, where all the Kontainer media entities are deleted.