Document DAST API scanner Peach API

Problem

The Peach API scan engine will be used for DAST API scans starting in 14.0. As part of the switch over, documentation will need to be updated.

Proposal

Split the existing documentation into two parts, DAST website scanning, and DAST API. The rational is the documentation will not overlap and would end up with a very long single page making it hard for users to locate relevant information.

The existing API Fuzzing documentation can be reused for DAST API, lowering the amount of work that will be needed.

• Split up existing documentation into two parts
  • Provide a link from the website docs to the API docs
• Leverage existing documentation
• Navigation link (https://docs.gitlab.com/ee/development/documentation/site_architecture/global_nav.html)