Importer: Handle Additional Gardener Mediatypes

Context

During the course of: &5523 (closed) some imports are failing due to unknown gardener mediatypes.

Solution

We should add the following mediatypes:

• application/vnd.gardener.cloud.cnudie.component-descriptor.v2+yaml+tar
• application/vnd.gardener.landscaper.blueprint.v1+tar+gzip
• application/json