feat: Sign Out Functionality

[JennaXiao3]

Description

What is the purpose of your change?

• implement the modal when sign out button is clicked and apply sign out functionality

What areas of the application does this change impact? (changes API, folder structure, etc)

• a new component SignOutButton.jsx is created

What features/fixes are deferred/not handled in this PR?

• currently, it is on the Test Page, so it needs to be put on the accounts page later

Checklist

• [ ] Adds unit tests
• [ ] Has a work item linked to the PR

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[leafie8]

lgtm!

[JennaXiao3]

Note to self: once signout, remember user's info from local storage