feat: Add Arc + Fleet hybrid setup for DocumentDB portal visibility

[hossain-rayhan]

Summary

Adds a new deployment guide for setting up DocumentDB across hybrid environments (AKS + on-premises) using Azure Fleet Manager. This enables Azure Portal visibility for all DocumentDB installations without requiring Azure extension registration.

Motivation

Customers need to track DocumentDB Kubernetes operator installations across diverse environments (cloud and on-prem) for billing and management purposes. This solution provides immediate portal visibility while the full Azure Arc extension integration is being developed.

What's Included

New: documentdb-playground/arc-hybrid-setup-with-fleet/

File	Purpose
README.md	Complete step-by-step guide (9 phases)
AGENT-INSTRUCTIONS.md	Copilot agent instructions for assisted setup
documentdb-instance.yaml	Sample DocumentDB CR for deployment
setup-fleet-hub.ps1	PowerShell script for Fleet + AKS creation
setup-arc-member.ps1	PowerShell script for Arc-enabling clusters
setup-arc-member.sh	Bash script for Kind cluster creation
cleanup.sh	Resource cleanup script

Updated: docs/designs/azure-arc/azure-arc-integration-plan.md

• Added reference to arc-hybrid-setup-with-fleet/ as interim solution

Architecture

Azure Fleet Manager (hubless)
├── AKS Member (native portal visibility)
└── Arc Member (Kind/on-prem with token-based portal access)
└── DocumentDB Operator + Instance on both

Key Features

• No extension registration required - uses vanilla Helm deployment
• Dual-environment workflow - handles corporate Conditional Access Policy restrictions
• Complete portal visibility - Fleet, AKS, and Arc portals all show deployments

Testing

Manually validated end-to-end:

• Fleet hub creation
• AKS cluster creation and Fleet join
• Kind cluster Arc-enable and Fleet join
• DocumentDB operator deployment on both clusters
• DocumentDB instance deployment on both clusters
• Portal visibility confirmed (AKS + Arc + Fleet)

[Copilot]

Pull request overview

Introduces initial scaffolding for deploying the DocumentDB Kubernetes Operator via Azure AKS/Arc Extensions, including a draft extension manifest, Arc-specific Helm values, local testing script, and supporting documentation/design plan.

Changes:

• Added Azure Arc extension manifest (extension.yaml) and Arc override values (values-arc.yaml) for Helm-based deployment.
• Added a Kind-based local test script to simulate Arc extension install flows.
• Added extension README plus a detailed Azure Arc integration design/rollout plan.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 17 comments.

Show a summary per file

File	Description
operator/arc-extension/values-arc.yaml	Adds Arc-oriented Helm values overrides for extension deployments
operator/arc-extension/test-arc-extension.sh	Adds local Kind + Arc testing harness for installation/verification/cleanup
operator/arc-extension/extension.yaml	Adds draft Azure extension manifest and release train definitions
operator/arc-extension/README.md	Adds end-user installation/configuration/troubleshooting guide
docs/designs/azure-arc/azure-arc-integration-plan.md	Adds detailed two-phase Arc integration + billing plan