ARI: Add events for Contact and Peer Status changes

This patch adds support for receiving events regarding Peer status changes
and Contact status changes. This is particularly useful in scenarios where
we are subscribed to all endpoints and channels, where we often want to know
more about the state of channel technology specific items than a single
endpoint's state.

ASTERISK-24870

Change-Id: I6137459cdc25ce27efc134ad58abf065653da4e9