chore: Initialize Cypress before secondary domain page loads

[chrisbreiding]

• Closes Multidomain: Better coordinate timing when secondary domain is visited #16778

User facing changelog

n/a - This is work for multidomain, targeting a feature branch

Additional details

This is preliminary work, required for #16773, making it possible to override DOM properties and methods before the secondary domain AUT page loads.

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[chrisbreiding]

This is a temporary measure to enable setting up the cross-domain bridge iframe. Once we tackle #17252, we'll look ahead to the cy.switchToDomain command and this will no longer be required.