api [nfc]: Rename streamPostPolicy to channelPostPolicy in Channel

Fixes parts of zulip#631

Author: Khader-1

lib/api/model/model.dart

@@ -319,8 +319,8 @@ class Channel {
   final bool historyPublicToSubscribers;
   final int? messageRetentionDays;
 
-  final StreamPostPolicy streamPostPolicy;
-  // final bool isAnnouncementOnly; // deprecated for `streamPostPolicy`; ignore
+  final StreamPostPolicy channelPostPolicy;
+  // final bool isAnnouncementOnly; // deprecated for `channelPostPolicy`; ignore
 
   // TODO(server-6): `canRemoveSubscribersGroupId` added in FL 142
   // TODO(server-8): in FL 197 renamed to `canRemoveSubscribersGroup`
@@ -346,7 +346,7 @@ class Channel {
     required this.isWebPublic,
     required this.historyPublicToSubscribers,
     required this.messageRetentionDays,
-    required this.streamPostPolicy,
+    required this.channelPostPolicy,
     required this.canRemoveSubscribersGroup,
     required this.streamWeeklyTraffic,
   });
@@ -417,7 +417,7 @@ class Subscription extends Channel {
     required super.isWebPublic,
     required super.historyPublicToSubscribers,
     required super.messageRetentionDays,
-    required super.streamPostPolicy,
+    required super.channelPostPolicy,
     required super.canRemoveSubscribersGroup,
     required super.streamWeeklyTraffic,
     required this.desktopNotifications,

lib/api/model/model.g.dart

@@ -78,7 +78,7 @@ void main() {
       'is_web_public': false,
       'history_public_to_subscribers': true,
       'message_retention_days': null,
-      'stream_post_policy': StreamPostPolicy.any.apiValue,
+      'channel_post_policy': StreamPostPolicy.any.apiValue,
       // 'can_remove_subscribers_group': null,
       'stream_weekly_traffic': null,
     });

test/api/model/model_test.dart

@@ -160,7 +160,7 @@ Channel stream({
   bool? isWebPublic,
   bool? historyPublicToSubscribers,
   int? messageRetentionDays,
-  StreamPostPolicy? streamPostPolicy,
+  StreamPostPolicy? channelPostPolicy,
   int? canRemoveSubscribersGroup,
   int? streamWeeklyTraffic,
 }) {
@@ -175,7 +175,7 @@ Channel stream({
     isWebPublic: isWebPublic ?? false,
     historyPublicToSubscribers: historyPublicToSubscribers ?? true,
     messageRetentionDays: messageRetentionDays,
-    streamPostPolicy: streamPostPolicy ?? StreamPostPolicy.any,
+    channelPostPolicy: channelPostPolicy ?? StreamPostPolicy.any,
     canRemoveSubscribersGroup: canRemoveSubscribersGroup ?? 123,
     streamWeeklyTraffic: streamWeeklyTraffic,
   );
@@ -208,7 +208,7 @@ Subscription subscription(
     isWebPublic: stream.isWebPublic,
     historyPublicToSubscribers: stream.historyPublicToSubscribers,
     messageRetentionDays: stream.messageRetentionDays,
-    streamPostPolicy: stream.streamPostPolicy,
+    channelPostPolicy: stream.channelPostPolicy,
     canRemoveSubscribersGroup: stream.canRemoveSubscribersGroup,
     streamWeeklyTraffic: stream.streamWeeklyTraffic,
     desktopNotifications: desktopNotifications ?? false,