Confirms an unconfirmed membership so it starts billing, and sends the patient the membership created email.
Confirming an already confirmed membership is a no-op.
Memberships synced from a network are read-only for the affiliate practice, with one exception: when the network
requires affiliates to confirm memberships, the affiliate may update the unconfirmed synced copy and confirm it
with this endpoint, and the network's record is confirmed along with it. Any other change to a synced membership
returns 409 "Contact the network to change this membership".