Add to db.serverStatus().metrics

changeStreams: {
	cluster: 0,
	database: 2, 
	collection: 3,
	showExpandedEventsTrue: 0,
	fullDocumentBeforeChange: {
		required: 1,
		whenAvailable: 0
	},
	fullDocument: {
		required: 0,
		whenAvailable: 0,
		updateLookup: 0
	},
	pipeline: 2
}

I discovered that internal stages for change streams like '$_internalChangeStreamAddPostImage' are only tracked in sharded clusters so we'll not have visibility into usage on replica sets, therefore I suggest tracking all the interesting options in a dedicated section.