[ADD] Added scrolledToEndPublisher. This sends event when the list …

…is scrolled to the end

Sources/ChatUI/Publishers/ScrolledToEndPublisher.swift

@@ -0,0 +1,30 @@
+//
+//  ScrolledToEndPublisher.swift
+//  
+//
+//  Created by Jaesung Lee on 2023/03/19.
+//
+
+import Combine
+
+// TODO: Unstable
+
+/**
+ The publisher that sends event when the list is scrolled to the end.
+ 
+ ```swift
+ // How to publish
+ scrolledToEndPublisher.send(true)
+ ```
+ ```swift
+ // How to subscribe
+ .onReceive(scrolledToEndPublisher) { isEnded in
+    if isEnded {
+        loadMoreMessages()
+    }
+ }
+ ```
+ 
+ - Important: This publisher is the beta feature.
+ */
+public var scrolledToEndPublisher = PassthroughSubject<Bool, Never>()