Include link to VTA on "Sign in" page

[ghengeveld]

From AP-4118

What

For users that have VTA setup on their project, but aren't familiar with how/why it works, add a "Learn more" link to goes to the VTA marketing landing page.

Why

The use case I'm thinking of is when a tech lead sets up a project and an engineer, who might not be familiar with it, tries it out themselves for the first time.

[MichaelArestad]

We need to add a "toolbar" as shown in the onboarding mockups. In the prototype, the action button on the top right links to the Visual Tests marketing website. It should look like this: