[Umbrella] Add webhook for validation

[kerthcet]

🚀 Feature Description and Motivation

Webhook is used for CRD validations, and will fail fast compared to runtime validation.

Use Case

Once CRD is not right configured, fail fast.

• webhook framework
• add integration tests to CI && separate with E2E tests
• ModelAdapter
• PodAutoscaler
• KVCache
• RayclusterFleet
• RayclusterReplicaset

Proposed Solution

No response

[kerthcet]

/assign

[Jeffwan]

We can discuss more details on the webhook usage. In the examples, we just use huggingface models for simplicity. However, in real world, most users has to fetch weights from S3 like object storage.

The challenge at this moment is AIBRix doesn't have any orchestration support to hide those details like llamaz or kubeAI.
As a mid term solution. I am thinking whether we can leverage webhook to convert more model configuration from annotations to specs fields like inject sidecar container for model downloading etc. that will fill the gap of missing model orchestration.