[Documentation] Centralize Prerequisite and API Documentation

[aghassemlouei]

Description of Documentation Need

The bootstrapping process requires manual enabling of various APIs (Cloud Resource Manager, Billing, Identity, Service Networking) and manual IAM permission grants, which are currently scattered or missing.

Target Audience

Operators, Developers, and System Administrators.

Proposed Location

A new file named docs/prerequisites.md or updated in fast/docs/README.md.

Content Outline / Draft

1. Required initial GCP Organization setup (Domain verification).
2. Creation of the initial bootstrapping project.
3. List of all APIs to enable prior to running Terraform.
4. Explicit list of roles required for the Terraform runner service account (e.g., roles/billing.admin, roles/orgpolicy.policyAdmin).

Compliance Context (if applicable)

Proper IAM documentation is required for passing FedRAMP System Security Plan (SSP) audits.

Additional Context

This was explicitly requested in the legacy Feature Braindump from 2023.