Add cloudback.it to trusted image domains list

[elv1s42]

Cloudback is a SaaS providing automatic daily backups and instant restores of GitHub repositories, metadata, and LFS. The service is available via GitHub Marketplace. The domain of the service is cloudback.it.

One of the features of Cloudback is a backup status badge, which is used to display the repository backup status. Please see the badge example below:

According to the NuGet documentation, there is a list of allowed domains for images and badges.

We would like to add the cloudback.it domain to the allowed domains list.

Thank you!

Addresses https://github.com/NuGet/NuGetGallery/issues/9942

[erdembayar]

@lyndaidaii Could you please review this PR?

[lyndaidaii]

Thank you for your work. I reviewed this domain's privacy policy and security concerns. Overall, looks good. Thanks.