Add a permission to generate ai media images

@thejimbirch Permission is currently controlled by the Image: Create new media or Create media permissions which can be granted or revoked for different roles.

I think you're asking for the ability to allow an editor to upload an image, but not be allowed to generate an AI image? Yes?

I'm not sure how much value this would add since the workaround would be there: the editor could just upload an AI generated image from another system. And then we lose out on the benefits of doing this within Drupal: e.g. having the filename note that the image is AI generated, control over providers/models, etc.

Here's a use case:

We run a fairly substaintial site and are currently testing/experimenting AI features. We have a role, "Tester", which we use to allow select members to test new features before releasing them more generally.

These are external people who we would not invite to a staging server, for example, but rather end-users who have been selected to participate in testing.

In this case, we need a way to restrict access to this great feature until we have seen it in action.

Attached is a patch that provides a permission to see/select "Generate Image with AI" from the select element. Probably not exactly what everyone would want, but fits our use case well.

My scenario is a higher ed university site that has a main site staff, and 500+ group sites. We would want so media creation for the main site staff, but do not want to share the Ai tokens with all the group sites.