feat: add initContainers support to RisingWaveNodePodTemplateSpec

[stex-docto]

What's changed and what's your intention?

This PR adds standard Kubernetes initContainers support to RisingWaveNodePodTemplateSpec.

Summary:

• Add InitContainers []corev1.Container field to RisingWaveNodePodTemplateSpec struct
• Wire the field through to the PodSpec in the object factory
• Regenerate deepcopy functions, CRD manifests, and API documentation

How it works:

• Follows the exact same pattern as the existing AdditionalContainers field
• Uses standard corev1.Container type from Kubernetes API
• Init containers are passed directly to the PodSpec's InitContainers field

Why it's needed:

• Init containers are a standard Kubernetes feature for running setup tasks before main containers start
• Common use cases: waiting for dependencies, initializing volumes, running migrations, etc.

Checklist

• I have written the necessary docs and comments
• I have added necessary unit tests and integration tests

Refer to a related PR or issue link (optional)

N/A