Docs: Define prerequisites for running the deploy-ctf workflow

[netr0m]

Describe Problem

Requirements include:

• Service principal
  • with permission to create resources (relates to Identify minimal set of Azure permissions required to deploy #57)
  • with federated credential grants for
    • the specific branch(es)
    • the specific environment(s)
• Organization/repository/environment variables and secrets required to run

Suggest Solution

Document the requirements

Additional Details