Fix ycrv to allow raw display and export when source is FRED

[montezdesousa]

Description

This PR fixes the --raw and --export outputs when ycrv --source FRED --raw --export csv is used. Currently, those flags only work for the default source investpy. If user picks FRED he cannot display raw data or export it to csv.

• Summary of the change / bug fix.
• Relevant motivation and context.

Test:
ycrv --source FRED -d 2021-01-04 --raw --export csv

Others

• I have performed a self-review of my own code.
• My code passes all the checks pylint, flake8, black, ... To speed up development you should run pre-commit install.
• New and existing unit tests pass locally with my changes. You can test this locally using pytest tests/....

[jmaslek]

Should we include logic that if a country is selected AND fred source, that it won't work. Namely

ycrv -c canada --source FRED

gives US yield curve