Logo-only header for QuickSight page. (PP-1720)

[tdilauro]

Description

Enables a logo-only (no navigation) header and uses it for the QuickSight Dashboard page.

This PR also fixes up some of the testing infrastructure to allow the jest/react testing library framework tests to:

• support tests that involve (sometimes transitively) the Footer component (by adding the TOSContextProvider into the component wrapper utilities;
• support tests involving the Header component -- specifically, loading the logo via require or import (by adding mock support for assets).

The key changes are in:

• src/components/Header.tsx
• src/components/QuicksightDashboardPage.tsx
• tests/jest/components/QuicksightDashboard.test.tsx

Motivation and Context

• Reduce user confusion and accidental navigation.
• Help prevent unnecessary consumption of QuickSight sessions.

[ Jira PP-1720]

How Has This Been Tested?

• Manual local testing, using a stand-in page to avoid using up QuickSight sessions.
• Tests pass locally.
• CI tests for branch pass.

Checklist:

• N/A - I have updated the documentation accordingly.
• All new and existing tests passed.

[ray-lee]

Looks good to me!