Switchboard Onboarding Flow - Prod Readiness Review

This MR introduces the Production Readiness document for the Switchboard Onboarding Flow.

Note: This delivery does not fit neatly into the Prod Readiness Review process as Switchboard is a standalone application allowing users to onboard to Dedicated. It does not interact with gitlab.com or have the usual dependencies

The Switchboard application allows new Dedicated customers to create and configure their Dedicated instance reducing operational cost on the Environment Automation team. In the future external customers will be able to configure existing tenant instances but this MR covers the Onboarding Flow functionality.

The document includes a checklist that is coming from the Production Readiness Template. We don't have to answer all questions but do our best.

Related issue: #86 (closed)