Move Developer onboarding to separate page
Move the Developer onboarding on https://about.gitlab.com/handbook/general-onboarding/ to https://about.gitlab.com/handbook/developer-onboarding/
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Move the Developer onboarding on https://about.gitlab.com/handbook/general-onboarding/ to https://about.gitlab.com/handbook/developer-onboarding/