feat: implement strict multi-zone pod distribution for StatefulSets (PSCLOUD-64)

[abhikumar2204]

Adds comprehensive multi-zone pod distribution to prevent StatefulSet quorum
loss during zone failures in AKS, EKS, and GKE clusters.

Features:

• Balanced topology spread constraints (maxSkew: 1) for optimal zone distribution
• Host-level anti-affinity to prevent multiple pods on same node
• Direct transformer application with single-zone compatibility
• Dedicated nodepool restriction for stateful workloads
• Configurable per-service (RabbitMQ, PostgreSQL) enablement

Changes:

• Add multi-zone transformers with balanced constraints
• Implement direct transformer application (simplified from zone detection)
• Add nodepool restriction with agentpool=stateful requirement
• Update VDM task pipeline to include multi-zone distribution
• Add comprehensive configuration variables with sensible defaults
• Update documentation with usage examples and behavior explanations

Transformers added:

• rabbitmq-zone-distribution.yaml (balanced multi-zone)
• postgres-zone-distribution.yaml (balanced multi-zone)
• multi-zone-pod-distribution.yaml (general StatefulSets)
• rabbitmq-single-zone-distribution.yaml (single-zone fallback)
• postgres-single-zone-distribution.yaml (single-zone fallback)

Configuration variables:

• V4_CFG_MULTI_ZONE_ENABLED (default: true)
• V4_CFG_MULTI_ZONE_RABBITMQ_ENABLED (default: true)
• V4_CFG_MULTI_ZONE_POSTGRES_ENABLED (default: true)
• V4_CFG_STATEFUL_NODEPOOL_RESTRICTION (default: true)

Technical Implementation:

• Topology spread: maxSkew: 1 with DoNotSchedule for balanced distribution
• Node affinity: agentpool=stateful label restriction
• Host distribution: maxSkew: 1 with DoNotSchedule for node-level spreading
• Graceful degradation: Works in both single-zone and multi-zone clusters

Validation Results:

• RabbitMQ (3 replicas) distributed across centralus-1, centralus-2, centralus-3
• Consul (3 replicas) distributed across centralus-1, centralus-2, centralus-3
• Redis (2 replicas) distributed across centralus-2, centralus-3
• PostgreSQL instances distributed across multiple zones

Resolves: Multi-zone StatefulSet quorum protection requirements (PSCLOUD-64)
Supports: AKS, EKS, GKE multi-zone and single-zone deployments
Backward compatible: Works with existing deployments without configuration changes