Is your feature request related to a problem? Please describe.
Related to : #16609

Describe the solution you'd like
It would be really great if we can easily extend the link format. Adding "rel" attributes value requires us to create a new format and deregister the core one. There's a need for option to add toggles on the link options as well.

Describe alternatives you've considered
Right now I've created a new link format on EditorsKit. But I don't want this solution of mine to cause any issues in the future if in any case there will be API changes. Thanks!