Update SaaS trial header to include the tier "Gold"

Problem

Currently, a user can enter the SaaS trial flow from multiple locations from about.gitlab.com to a multitude of CTAs in the product, depending on where a user is coming from they may not be aware they are trialing the Gold tier.

Related feedback we've received in the Slack product channel based on our new "start a trial" option in the top right dropdown "I don't know what I'm starting a trial of".

Solution

We should update the header text on the following pages to include the tier "Gold".

User sign up	Trial sign up form
Current header "Start a Free Trial"	Current header "Start a Free Trial"
New header "Start a Free Gold Trial"	New header "Start a Free Gold Trial"