Adjust styling on /company page for automatic_trial_registration

What does this MR do and why?

Related to #409406

Adjust styling of the description text for the candidate experience of automatic_trial_registration experiment according to UX review.

1. Increase top margin to 8px
2. Change text color to gray-500

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Start local GDK simulating SaaS.
2. In rails console, enable the experiment by Feature.enable(:automatic_trial_registration)
3. Go through register and on sign_up/welcome page, select My company or team and Create a new project
4. Land on the /sign_up/company form page and observe.

MR acceptance checklist

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