fix: changed currency exchange API to frankfurter (#15958)
fix: changed currency exchange API to frankfurter (#15958)

- Switched to Frankfurter's public API (frankfurter.app) from
self hosted API (frankfurter.erpnext.org)
gsnbng/erpnext,gsnbng/erpnext,gsnbng/erpnext,gsnbng/erpnext