MM-52600: [Shared Channels] Shared channels do not sync channel membership (#30976)

server/channels/app/platform/shared_channel_service_iface.go

@@ -23,6 +23,7 @@ type SharedChannelServiceIFace interface {
 	CheckChannelNotShared(channelID string) error
 	CheckChannelIsShared(channelID string) error
 	CheckCanInviteToSharedChannel(channelId string) error
+	HandleMembershipChange(channelID, userID string, isAdd bool, remoteID string)
 }
 
 type MockOptionSharedChannelService func(service *mockSharedChannelService)
@@ -77,3 +78,7 @@ func (mrcs *mockSharedChannelService) SendChannelInvite(channel *model.Channel,
 func (mrcs *mockSharedChannelService) NumInvitations() int {
 	return mrcs.numInvitations
 }
+
+func (mrcs *mockSharedChannelService) HandleMembershipChange(channelID, userID string, isAdd bool, remoteID string) {
+	// This is a mock implementation - it doesn't need to do anything
+}