[Bugfix/Stocks/KeyMetricsExport] Add export call to FA key metrics controller

[asymness]

Description

• Summary of the change / bug fix.
  The stocks/fa/key call does not handle the --export parameter even though it is documented.
• Link # issue, if applicable: [Bug] /stocks/fa/key: --export does not function. #2181
• Screenshot of the feature or the bug before/after fix, if applicable.
  Before

**After**

• Relevant motivation and context: Prior to this change, user can not export key metrics of a stock.
• List any dependencies that are required for this change: N/A

How has this been tested?

• Please describe the tests that you ran to verify your changes.
  Running stocks >> load goog >> fa >> key --export xlsx after the change saves an export file which does not get exported without this change.

• Provide instructions so we can reproduce.
  Running stocks >> load goog >> fa >> key --export xlsx, no file is exported.

• Please also list any relevant details for your test configuration.
  N/a

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.
• 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/....

[DidierRLopes]

Amazing! Thank you!