subscribe
Subscribes to the external presence updates of a personal contact from the specified contactId.
This function validates that the contact exists and belongs to a Personal source before establishing the subscription. It uses a shared subscription mechanism to optimize resources.
Return
An ExternalPresenceSubscription to manage the lifecycle of the presence stream. If the contact is not found or is not a personal contact, a NoOpExternalPresenceSubscription is returned.
Parameters
contact
Contact Id to be subscribed to.