Wrong mediaType reported by REST API for forms #3003
Description
Describe the bug
The app-repository/deployments/{id}/resources REST API returns mediaType as text/xml for .form files.
Expected behavior
Return application/json, which is the correct media type for forms.
Additional context
Found in v6.6.0 and further verified in master branch of source DefaultContentTypeResolver
Additionally found that .app files content type is not included in the common class but in AppDeploymentResourceResource so that should probably be centralised too.