Improve Forex Helper

[colin99d]

Description

Fixes #3235

Currently the forex_helper uses the stocks_helper instead of calling yfinance on its own. This creates a lot of needless errors. I switched the forex_helper to just calling yf.download directly. This reduced the amount of code needed, and allows for all intervals to be called for yfinance.

Also makes the functionality to get the interval smarter for the SDK.

How has this been tested?

• Please describe the tests that you ran to verify your changes.
• Provide instructions so we can reproduce.
• Please also list any relevant details for your test configuration.

• Make sure affected commands still run in terminal
  • python terminal.py "forex/load USDHUF -i 3month"
  • python terminal.py "forex/load USDHUF -i 1day --source AlphaVantage"
• Ensure the SDK still works
  • openbb.forex.load("USD", "GBP", interval="1day")
• Check any related reports
  • python terminal.py reports/forex USDGBP

Checklist:

• Update our Hugo documentation following these guidelines.
• Update our tests following these guidelines.
• Make sure you are following our CONTRIBUTING guidelines.
• If a feature was added make sure to add it to the corresponding scripts file.

Others

• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.