Update the association between a campaign and a message.

Submitting a campaignid moves the message to that campaign, which requires access to both the campaign the message belongs to and the campaign it is moved to.

Only campaignid, messageid and percentage may be written. Every other field of a campaign message is a counter maintained by the sending code, and is ignored when it is submitted.

The request needs the campaigns feature to be enabled for the account, and the caller has to have access to the campaign, otherwise the request is a 403. A body without a campaignMessage object is a 400.