Dark launch docs: Migrate from PW current source of truth into better location for CMS ongoing documentation

[jilladams]

User Story or Problem Statement

As a content editor, I need to understand the options for testing CMS content pre-production.

Description or Additional Context

In 2022, Public Websites built a mechanism to allow "dark launching" CMS content, for usability testing. This "product" should now transition to CMS team for long-term enhancement & maintenance, or to EOL.

Background re: transitioning to CMS Team: https://dsva.slack.com/archives/CT4GZBM8F/p1698696734566799

Existing docs, in PW team products docs: https://github.com/department-of-veterans-affairs/va.gov-team/tree/master/products/public-websites#shadow--dark-launches-of-content

• The original use case here was for usability testing CMS content in Staging, since Tugboat is not publicly accessible.
• Staged Content entity subqueue in the CMS. Adding nodes to this queue means they will only be built for Staging, not Production.
• Dark launch request issuetemplate: currently gets assigned to Public Websites -- includes a runbook for managing the steps to dark launch a new product
• Ryan Koch and Daniel Sasser helped build this. We've used it one time, for a new Form online tool that never did launch due to contract transition. It's really only fleshed out for new products / pages, and not really for handling iterative launches or existing CMS content.

Acceptance Criteria

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[jilladams]

Went ahead and updated assignment / team info in the issuetemplate for this: https://github.com/department-of-veterans-affairs/va.gov-cms/blob/main/.github/ISSUE_TEMPLATE/dark-launch.md

[BerniXiongA6]

@EWashb @ndouglas I'll add this to our sync this week