feat: add --transfer-accounts flag for 2UP shared account deduplication

[alecpirillo]

Adds a --transfer-accounts option that accepts account mappings used only for transfer payee resolution without syncing those accounts. Very useful feature for when you are running this sync multiple times across multiple up users with UP connector. For example syncing both partners individual up accounts, with the new flag you can specify which accounts are represented in other sync runs, allowing automatic identification as transfers. Means no manual de-duplication in actual. 2 new tests - 1 to validate the prior feature for joint de-duplication, and one for this use case.

Not sure if its useful enough to earn its own section in the read me - feel free to remove.

[alecpirillo]

Consider that is a very specific use case and may not be appropriate to bundle into an agnostic sync tool. Thinking about it this morning, this feature could be expanded to be more universal. It could be used to link transactions to other accounts in actual, not just up specific transfers which is my use case. This is capability that can be achieved in actual with rules (and merging any dups manually), but it does greatly simplify on boarding for new users who decide to use the feature and makes sync smarter as a whole.