Targeting with TO Field

// Add the activity to Eric's feed and to Jessica's notification feed
	activity := stream.Activity{
		Actor: "user:Eric",
		Verb:  "tweet",
		Object: "tweet:id",
		To: []string{
			"notification:Jessica", // In production use user ids, not their usernames
		},
		Extra: map[string]any{
			"message": "@Jessica check out getstream.io it's so dang awesome.",
		},
	}
	_, err := userFeed.AddActivity(context.TODO(), activity)
	if err != nil {
		panic(err)
	}

// The TO field ensures the activity is send to the player, match and team feed
	activity := stream.Activity{
		Actor: "Player:Suarez",
		Verb:  "foul",
		Object: "Player:Ramos",
		To: []string{
			"team:barcelona",
			"match:1",
		},
		Extra: map[string]any{
			"match": map[string]any{
				"name": "El Clasico",
				"id":  10,
			},
		},
	}
	_, err := playerFeed.AddActivity(context.TODO(), activity)
	if err != nil {
		panic(err)
	}

// Remove all old targets and set new ones (replace):
	newTargets := []string{"user:1", "user:2"}

	_, err := userFeed.UpdateToTargets(context.TODO(), activity, stream.WithToTargetsNew(newTargets...))
	if err != nil {
		panic(err)
	}

	// Add some targets and remove some others:
	add := []string{"user:1", "user:2"}
	remove := []string{"user:3", "user:4"}

	_, err := userFeed.UpdateToTargets(
		context.TODO(),
		activity,
		stream.WithToTargetsAdd(add...),
		stream.WithToTargetsRemove(remove...),
	)
	if err != nil {
		panic(err)
	}