feat: add elevation and centerTitle to ThreadHeader and ChannelListHeader

packages/stream_chat_flutter/lib/src/channel_header.dart

@@ -170,7 +170,7 @@ class ChannelHeader extends StatelessWidget implements PreferredSizeWidget {
                     ),
                   ),
                 ],
-            centerTitle: _getEffectiveCenterTitle(theme),
+            centerTitle: centerTitle,
             title: InkWell(
               onTap: onTitleTap,
               child: SizedBox(
@@ -202,24 +202,4 @@ class ChannelHeader extends StatelessWidget implements PreferredSizeWidget {
 
   @override
   final Size preferredSize;
-
-  /// Returns the effective center title for the current theme and platform.
-  ///
-  /// This code is aligned with the [AppBar]'s [AppBar.centerTitle].
-  bool _getEffectiveCenterTitle(ThemeData theme) {
-    if (centerTitle != null) return centerTitle!;
-    if (theme.appBarTheme.centerTitle != null) {
-      return theme.appBarTheme.centerTitle!;
-    }
-    switch (theme.platform) {
-      case TargetPlatform.android:
-      case TargetPlatform.fuchsia:
-      case TargetPlatform.linux:
-      case TargetPlatform.windows:
-        return false;
-      case TargetPlatform.iOS:
-      case TargetPlatform.macOS:
-        return actions == null || actions!.length < 2;
-    }
-  }
 }