Add Actor migration

[pfefferle]

This adds the fields that are required for the ActivityPub target domain.

Changes proposed in this Pull Request

• https://docs.joinmastodon.org/user/moving/
• https://blog.joinmastodon.org/2019/06/how-to-migrate-from-one-server-to-another/

[jessLundie]

Thank you so much for this!

A few questions:

• Will we also need to set the as:movedTo? in a similar way here?
• In addition to the changes here and the ActivityPub plugin patch, will we also need to log in to Mastodon to make the changes within Mastodon as shown in the documentation you linked? Or does ActivityPub basically "push" the changes to Mastodon?
• What are the testing steps to confirm everything is forwarding correctly once we have it all flipped over?

[pfefferle]

Hey @jessLundie, this is the only change we have to add to the target site.

I am now preparing the extension for the old blog, that triggers the move and adds the movedTo. I decided to not build that directly into the plugin (yet), because it's harder than I thought to have a generic solution.