transfers: admin command to rebuild and submit files for a time window

[adamdecaf]

PayGate Version: v0.9.0-dev

We need to have an option to rebuild and/or resubmit all pending files. This allows us to save ourselves if merging (or the merged) ACH files fails during a cutoff window. I'm thinking of two admin endpoints, see below.

Merging

PUT /files/merge[?wait]
This endpoint would trigger another iteration of merging (inside a new directory under ./storage/) from all the pending files. These could then be uploaded later on (or downloaded).

PUT /files/upload-individual[?wait]
This endpoint would upload all pending ACH files to the SFTP server without merging them. While resulting in higher fees this would allow us to handle each Transfer as a unique upload.