Help users to replace their own key
Replacing a key for a user is a common task and should be easier. Essentially it's three steps:
- import the new key
- assign the fingerprint of the new key to the subscription
- delete the old key (optional)
Deleting the old key should only happen if X-DELETE-KEY is not listed as admin-only.
Users should be able to use this feature for their own subscription. Admins should be able to use it for any subscription.