Added mutation-specific rate limits for duplicate board and duplicate group mutations

Added mutation-specific rate limits, based on the number of API calls made within a minute for the following mutations:

• duplicate_group;
• duplicate_board;

The mutations above will have an additional rate limit of 40 mutations per minute. If you exceed this limit, you will receive a 429 HTTP response code with "Call limit exceeded for DuplicateGroup" or "Call limit exceeded for DuplicateBoard" error message.