Relies on https://joindin.jira.com/browse/JOINDIN-639.

Using the same endpoint, when the other party (speaker or event/site admin) POSTs a matching set of data (speaker display name, username) to an existing claim, activate the link by setting the speaker ID in the relevant row in talk_speaker.

The talk should then appear on the user's account and they will be linked from the talk page.

If the claim was approved by an organiser, email the speaker to let them know their claim has been approved.

Once successfully linked, the related row from pending_talk_claims should be deleted.