Add managing environment policies page under Administration #167

Description

Add a new page under Administration > Managing Environments that covers managing environment policies and how to attach them to environments.

The current Administration section has a "Managing Environments" group with only an overview page. The Getting Started section covers policies conceptually (getting_started/policies), and the Terraform Reference has kosli_policy and kosli_policy_attachment resources, but there is no Administration-level page for managing environment policies day-to-day.

Proposed scope

• Creating policies (CLI, API, Terraform)
• Viewing and versioning policies (policies are immutable; updates create new versions)
• Attaching policies to environments (including via kosli_policy_attachment Terraform resource)
• Detaching policies from environments
• Practical examples for common policy patterns (provenance, attestations, trail compliance)

Location

• File: administration/managing_environments/policies.md (or similar)
• Navigation: add under Administration > Managing Environments in config/navigation.json

Related resources

• getting_started/policies — conceptual overview
• getting_started/enforce_policies — enforcement overview
• terraform-reference/resources/policy — Terraform resource reference
• terraform-reference/resources/policy_attachment — Terraform attachment reference
• policy-reference/environment_policy — policy schema reference
• CLI: kosli attach-policy, kosli detach-policy, kosli create policy

Sub-issues

• Document attaching multiple environments to the same policy