feat: RESP3 notifications support & Hitless notifications handling [CAE-1088] & [CAE-1072] (#3418)

- Adds support for handling push notifications with RESP3. 
- Using this support adds handlers for hitless upgrades.

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Hristo Temelski <hristo.temelski@redis.com>

push/handler.go

@@ -0,0 +1,14 @@
+package push
+
+import (
+	"context"
+)
+
+// NotificationHandler defines the interface for push notification handlers.
+type NotificationHandler interface {
+	// HandlePushNotification processes a push notification with context information.
+	// The handlerCtx provides information about the client, connection pool, and connection
+	// on which the notification was received, allowing handlers to make informed decisions.
+	// Returns an error if the notification could not be handled.
+	HandlePushNotification(ctx context.Context, handlerCtx NotificationHandlerContext, notification []interface{}) error
+}