reorganize-configuration-guides to improve user journey through docs

General MR

Summary

• Reframed “Sample Production Configuration” as Production Considerations for GitLab, Vault, and Keycloak docs/configuration/production-package-considerations.md, with an explicit warning that it is not a complete production baseline.
• Split production considerations for GitLab, Vault and Keycloak into multiple docs. Creating a framework for additional future package specific production considerations.
• Moved the full ambient mission-application walkthrough into Tutorials docs/tutorials/ambient-mission-apps.md. Its substantive content was preserved.
• Left forwarding pages at both legacy paths so existing links and bookmarks remain useful.
• Updated navigation, indexes, migration guidance, ambient-mode resources, and backup/restore links to use the canonical pages.

Additional tutorial reorganization

• Split the 514-line ambient mission-application walkthrough into a focused tutorial series:
  • Overview and deployment-path selection
  • Shared ambient namespace, network policy, and authorization policy requirements
  • Deployment through the Big Bang packages key
  • Deployment through Argo CD
• Added prerequisites, reconciliation, verification, and cleanup steps to both deployment tutorials.
• Preserved the complete Parabol configuration and policy examples.
• Pinned the Parabol example to the immutable 4.0.6 tag instead of main.
• Added the argocd namespace to the example Argo CD Application.
• Moved the temporary sidecar-mode exception into the ambient configuration guide and explicitly disabled ambient enrollment before enabling sidecar injection.
• Retained the previous tutorial URL as a forwarding page and updated navigation and inbound links.

Relevant logs/screenshots

n/a

Linked Issue

Closes #3403 (closed)

Closes #3404 (closed)

Upgrade Notices

N/A