chore: Create a story for UnitInput component

[Devin-Apps]

Description

This pull request adds a Storybook story for the UnitInput component. The story renders the UnitInput component with several configurable properties, allowing users to interact with and test the component in isolation. The story adheres to the project's standards and provides a clear example of how the UnitInput component can be used.

Related issues

Manual testing steps

• Go to the latest build of storybook in this PR
• Navigate to the UnitInput component in the Components/UI folder.

Screenshots/Recordings

Pre-merge author checklist

• I’ve followed MetaMask Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

Devin Run

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[georgewrmarshall]

LGTM!

[georgewrmarshall]

This may need to be merged with develop to pass test-deps-audit

[metamaskbot]

No release label on PR. Adding release label release-12.2.0 on PR, as PR was added to branch 12.2.0 when release was cut.