Create Declarable CFPB Logo href

Description

Currently, the CFPB logo in the React DS has a hardcoded href pointing to cf.gov. Using the CFPB logo from the React DS, we've run into the issue of users being booted from the Metro2 tool when the logo is clicked. This will inevitably cause frustration and confusion, as users will expect to be routed back to the landing page for the Metro2 Evaluator Tool.

This PR seeks to implement a change which will turn the logo href into a prop that can be defined in every project that uses the React DS component. Additionally, the logo still defaults to cf.gov if no other href/url is specified.

Changes

href prop created for CfpbLogo, passed to Navbar and PageHeader
test file created for page header to include testing custom href and/or defaulting to cf.gov

How to test this PR

Pull branch and run yarn start. Navigate to Navbar and Page header pages and verify CFPB logo points to cf.gov
Create a story for either Navbar or PageHeader:
- Open file 'PageHeader.stories.tsx'
- Create an additional story that displays the CFPB logo with custom href export const CustomCFPBHref: Story = { args: { href: 'https://www.google.com' } };
- Go to PageHeader page in React DS and verify additional story was created. Click added CFPB logo (or hover above logo/link) and verify correct url
Check added test with yarn test and verify tests pass

Notes

Following the guidelines for adding unit tests, a PageHeader.test.tsx file was created.

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