Redesign old Guide pages

Created by: zlonko

This closes #5370 (closed). It reformats the remaining two Guide pages to conform to our new design standard.

Changelog

• Implements the GatedResourceLayout on /guides/continuous-developer-onboarding and /guides/dev-onboarding-how-is-it-unique
• Prettier update

Notes

• The copy in the Figma differs from what is in production. Fabiana comments that we should keep the copy that is in production.
• For the HubSpot forms, I still need to remove the titles ("Download the guide") and extend the width to 100%. I am waiting until eng review is complete to make these changes, as these same forms are in production!

Example of a form to be updated (duplicated title, not full-width):

Needs to match the correct format:

Test

1. Ensure prettier has standardized the proposed changes.
2. Navigate to /guides/continuous-developer-onboarding
3. Navigate to /guides/dev-onboarding-how-is-it-unique
4. Please check that the PDFs download on both pages after form submission