Add transaction summary method

[pazwicker]

Adds transaction summary method.

This method will be helpful in introducing another feature to allow getting all transactions. The transaction summary includes the total number of transactions in a Monarch account, which can be used to create a loop through transactions where the maximum number of iterations is determined by the total number of transactions in the account, also accounting for timeouts and limits.

[pazwicker]

@hammem whoops! Ran black on monarchmoney but not main. Just fixed.

[hammem]

Thanks, merged!