Add a retry mechanism for custom domains

[BjrInt]

This feature allow users to revalidate their custom domain if the DNS check has failed. It works by sending a new aggregate message with a timestamp (to force an update).

[BjrInt]

I am aware that duplicating the same content inside of the <StatusLabel> is not ideal, but we also need this content to be customized.
Maybe by putting a default content for the 3 possible variants that's replaced when children are passed.

I'm also aware of the weird pattern on the default value for an aggregate message that has no updated_at property.