Set user profile URL to creator URL if user owns a single creator

[Floppy]

To add to the list based on what @amdavidson says:

• [ ] Select the creator's preferred name and username by default during fediverse follows

This way when I get a follow notification on a mastodon instance that someone is following me, I can get redirected back to the creator page rather than the user's page.

This makes things more complex for a collective of Users assigned to a single Creator, so a UI option to select the Creator you want to follow as would be a great.

Originally posted by @matthewbadeau in #4352

[Floppy]

This needs an extra capability adding into federails - currently the profile method is expected to the name of a Rails router method, whereas this needs to be either a method call on the object itself or a lambda of some sort.