Support for podcasting 2.0 feature "license" tag.
Is your feature request related to a problem? Please describe
As Castopod is a modern podcast host that supports Podcasting 2.0, it should support as many tags as possible within the specification. License is a tag that allows a podcaster to tag a podcast with a license that helps listeners know what they can do with the content. Is it all rights reserved, or CC with Attribution, or something else.
https://github.com/Podcastindex-org/podcast-namespace/blob/main/docs/1.0.md#license
Describe the solution you'd like
MVP: On the podcast edit page, a drop-down of licenses in the SPDX list.
Iteration: Ability to specify a custom license with URL.
Describe alternatives you've considered
Including this in the custom RSS field is easy, but having explicit support for the tag will demonstrate support for the Podcasting 2.0 movement.
Additional context
It was @benjamin who proposed the tag in the first place. ;)