chore: Completing storybook for Flag component

[Golodhros]

Summary of Changes

Adds story for the Flag component

Documentation

CheckList

Make sure you have checked all steps below to ensure a timely review.

• PR title addresses the issue accurately and concisely. Example: "Updates the version of Flask to v1.0.2"
  • In case you are adding a dependency, check if the license complies with the ASF 3rd Party License Policy.
• PR includes a summary of changes, including screenshots of any UI changes.
• PR adds unit tests, updates existing unit tests, OR documents why no test additions or modifications are needed.
• In case of new functionality, my PR adds documentation that describes how to use it.
  • All the public python functions and the classes in the PR contain docstrings that explain what it does
• PR passes all tests documented in the developer guide

Signed-off-by: Marcos Iglesias miglesiasvalle@lyft.com

[allisonsuarez]

LGTM!