[Feature] Balance Of Payments For FRED

[deeleeramone]

1. Why?:

   • Expanding the macroeconomics data collection, this adds the BP6 data set published by the OECD, via FRED.

2. What?:

   • obb.economy.balance_of_payments(provider="fred", country="portugal")
   • All values are reported as $USD

3. Impact:

   • Expands the standard model, which should also be compatible with the OECD provider - if being added - as it is the same data, just forwarded through FRED.

4. Testing Done:

   • Various countries and start/end dates.
   • Not every country reports every field.