Configurable New Filename Format

[gary-roach]

When filing documents with Fava, the date is prepended to the filename. This is similar to the functionality of beancounts bean-file tool, but the format is not the same.

When using bean-file the file is renamed like this:
Original File Name: My File.csv
New File Name: YYYY-MM-DD.My_File_Name.csv

Fava renames files like this:
Original File Name: My File.csv
New File Name: YYYY-MM-DD My File Name.csv

I personally prefer the beancount way as I don't like spaces in my filenames. I know Fava lets me rename them manually, but would you be open to the default file rename pattern being configurable? As far as I can tell, it would require changes to frontend/src/reports/import/index.ts and frontend/src/document-upload.ts.