Support migrate module: Individual destination class

#1116408: Support migrate module: Destination handler class → is about adding a migration destination handler for redirect.

This issue is about adding one destination class, so we can create migration classes that only import redirects. I have a use case where I am not importing other entities at the same time, so this is the only clean way I could think to do it.

Patch following, naturally it started with the code on the other issue, but it's a different migration destination class.

PS: I though it will be clear to have it in a separate issue, but I could merge this into the other issue if one of the maintainers think it's better.