Refactor out header checks in homepage E2E tests

[dgodongm]

Description

Created validateHeader util module with helper methods similar to validateFooter, and updated homepage E2E tests to use these, adding distinct test for mobile as well.

Related Issue

121 - provides some E2E coverage instead of component as it seems there's technical impediment for the latter - see comments in this issue

Motivation and Context

Ensure more consistent approach between footer and header checks. And, adding some coverage for modal menu on mobile.

How Has This Been Tested?

Tested locally on Chrome

Screenshots (if appropriate):

n/a

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[dgodongm]

@chadstewart @marktnoonan What do you think of this refactoring, and additional mobile test?

[dgodongm]

Thanks @marktnoonan! @chadstewart - any feedback or are you good with merging?

[dgodongm]

@chadstewart @marktnoonan Can this be merged?

[marktnoonan]

@chadstewart this needs you to authorize the Vercel step. Or I can merge without that since it's just tests.

[dgodongm]

@chadstewart Friendly ping on this PR