[MM-16568] Migrate "User.SearchInChannel" to Sync by default (#11417)

* implemented migration to sync

* updated user.go to use explicit async approach

store/sqlstore/user_store.go

@@ -1303,15 +1303,17 @@ func (us SqlUserStore) SearchNotInChannel(teamId string, channelId string, term
 	})
 }
 
-func (us SqlUserStore) SearchInChannel(channelId string, term string, options *model.UserSearchOptions) store.StoreChannel {
-	return store.Do(func(result *store.StoreResult) {
-		query := us.usersQuery.
-			Join("ChannelMembers cm ON ( cm.UserId = u.Id AND cm.ChannelId = ? )", channelId).
-			OrderBy("Username ASC").
-			Limit(uint64(options.Limit))
+func (us SqlUserStore) SearchInChannel(channelId string, term string, options *model.UserSearchOptions) ([]*model.User, *model.AppError) {
+	query := us.usersQuery.
+		Join("ChannelMembers cm ON ( cm.UserId = u.Id AND cm.ChannelId = ? )", channelId).
+		OrderBy("Username ASC").
+		Limit(uint64(options.Limit))
 
-		*result = us.performSearch(query, term, options)
-	})
+	result := us.performSearch(query, term, options)
+	if result.Err != nil {
+		return nil, result.Err
+	}
+	return result.Data.([]*model.User), nil
 }
 
 var escapeLikeSearchChar = []string{