Show custom message when image repository deletion fails due to import

🔥 Problem

Similar to #352079 (closed).

We should not accept image repository destruction if the image repository is importing.

🚒 Solution

Don't allow the operation and display the same error as in #352079 (closed):

Image repository temporarily cannot be marked for deletion. Please try again in a few minutes. [More details](https://docs.gitlab.com/ee/user/packages/container_registry/#tags-temporarily-cannot-be-marked-for-deletion).