Feature: Add Multi-Architecture Docker Build Support

[gourishkb]

🔖 Feature description

We need to update the Docker build pipeline for cmd-admission-webhook-k8s to support multi-architecture image builds, specifically for linux/amd64 and linux/arm64 platforms.

🎤 Pitch

Why This Matters ?

• Enables usage of the image on ARM-based environments (e.g., Raspberry Pi, AWS Graviton, Apple M-series).

• Aligns with ongoing multi-arch compatibility efforts across all KubeSlice repositories.

• Improves flexibility and adoption across diverse environments.

✌️ Solution

Acceptance Criteria:

• Dockerfile updated to support cross-platform builds.

• Confirm compatibility by testing on at least one linux/arm64 environment.

Suggested Steps:

• Update Dockerfile for cross-architecture compatibility. refer to [https://github.com/kubeslice/kubeslice-controller/blob/master/Dockerfile](Dockerfile example) to understand how it is done in other KubeSlice repos
• Enable Docker Buildx in the CI workflow (i.e GitHub Actions)
• Test locally or in CI to validate builds for both amd64 and arm64.