Add support for querying for recurring merchants & transactions

[hammem]

Part of the response to a question that came up on Reddit: https://www.reddit.com/r/MonarchMoney/comments/180hb5j/comment/kpnqr4i/?context=3

Add functions to pull recurring merchants, as well as recurring transactions.

Make sure to document the process of how to reverse engineer the GraphQL calls in this issue discussion.