update for adding multiple members (#25128)

* update for adding multiple members

* fix unit test

* more test fixes

* add another unit test

* fix object passed by client4

* revert package-lock.json

* revert package-lock.json

* add length check

* limit size of lists in API requests

* revert package-lock

* add batching to front end

* add batching to front end

* fix bad merge

* update return type

* remove unnecessary permisssion check, add unit test

* fixes and add tests from review

* revert changes adding limits to other apis

* fixes

* clean-up from code review

* fix unit test call

* revert back to interface{}, fix unit test

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/public/model/client4.go

@@ -3730,6 +3730,23 @@ func (c *Client4) AddChannelMember(ctx context.Context, channelId, userId string
 	return ch, BuildResponse(r), nil
 }
 
+// AddChannelMembers adds users to a channel and return an array of channel members.
+func (c *Client4) AddChannelMembers(ctx context.Context, channelId, postRootId string, userIds []string) ([]*ChannelMember, *Response, error) {
+	requestBody := map[string]any{"user_ids": userIds, "post_root_id": postRootId}
+	r, err := c.DoAPIPost(ctx, c.channelMembersRoute(channelId)+"", StringInterfaceToJSON(requestBody))
+	if err != nil {
+		return nil, BuildResponse(r), err
+	}
+	defer closeBody(r)
+
+	var ch []*ChannelMember
+	err = json.NewDecoder(r.Body).Decode(&ch)
+	if err != nil {
+		return nil, BuildResponse(r), NewAppError("AddChannelMembers", "api.marshal_error", nil, "", http.StatusInternalServerError).Wrap(err)
+	}
+	return ch, BuildResponse(r), nil
+}
+
 // AddChannelMemberWithRootId adds user to channel and return a channel member. Post add to channel message has the postRootId.
 func (c *Client4) AddChannelMemberWithRootId(ctx context.Context, channelId, userId, postRootId string) (*ChannelMember, *Response, error) {
 	requestBody := map[string]string{"user_id": userId, "post_root_id": postRootId}