Feature: Add label-driven YurtHub installation controller

[SamyakBorkar]

What type of PR is this?

/kind feature

What this PR does / why we need it:

This PR implements automatic YurtHub installation/uninstallation based on node labels.

Problem: Currently, YurtHub requires yurtadm join, which:

• Doesn't work on existing Kubernetes nodes
• Is incompatible with third-party cluster management tools
• Requires manual intervention per node

Solution: New controller that watches for openyurt.io/is-edge-worker=true label and automatically:

• Creates Kubernetes Job to install YurtHub via node-servant
• Tracks installation status with node annotations
• Uninstalls when label is removed

Usage:

# Convert any node to edge node
kubectl label node <name> openyurt.io/is-edge-worker=true

# Revert back
kubectl label node <name> openyurt.io/is-edge-worker-

Why this matters:

✅ Works with ANY Kubernetes cluster/management tool
✅ No downtime or cluster rejoining needed
✅ Declarative and Kubernetes-native
✅ Scales to hundreds of nodes easily

Which issue(s) this PR fixes:
Fixes #2494

Special notes for your reviewer:
Implementation highlights:

• Reuses existing node-servant infrastructure (convert/revert commands)
• Disabled by default (opt-in via --enable-yurthub-installer=true)
• Comprehensive error handling and event emission
• Unit tests for controller logic included
• Full RBAC permissions defined

Documentation:

• Detailed proposal document: docs/proposals/20260122-label-driven-yurthub-installation.md
• Controller README: pkg/yurtmanager/controller/yurthubinstaller/README.md
• Usage examples: docs/examples/yurthub-auto-install-example.yaml

Testing:

File summary:

• 13 files changed, 1490 insertions
• Controller implementation: ~440 lines
• Unit tests: ~270 lines
• Documentation: ~500 lines
• Configuration integration: ~80 lines

Does this PR introduce a user-facing change?
Yes.

This PR introduces a label-driven mechanism that allows users to
automatically install or uninstall YurtHub on edge nodes by applying
or removing a Kubernetes node label.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud