Add ARM64 support for Helm installation in connectedk8s

[ashnanze]

Summary

• Bumps Helm version from v3.12.2 to v3.20.1.
• Detects host architecture via platform.machine() (maps aarch64/arm64 to arm64, defaults to amd64).
• Uses the detected architecture in all Helm artifact tags, download file names, and install paths (previously hardcoded to amd64).
• Adds _resolve_helm_pull_target() to resolve the correct OCI pull target: tries arch-specific tag first (helm-v3.20.1-linux-arm64), falls back to manifest list tag (helm-v3.20.1) with annotation-based matching.
• Ensures the versioned local download directory exists before saving the Helm archive.

Why

• Enables az connectedk8s connect to work on ARM64 machines by downloading the correct Helm binary.
• Previously, ARM64 hosts would download the AMD64 binary, which would fail to execute. 

Validation

• Built and installed the updated extension .whl.
• Validated behavior on an ARM64 VM.
• Validated behavior on an AMD64 VM.
• Both VMs successfully completed az connectedk8s connect.
• Confirmed the updated Helm installation flow works across both architectures.

Directory handling note

• This fix also addresses a latent path issue in Helm download setup.
• The download target file path is ~/.azure/helm/<version>/<archive-file>.
• Previous logic only created the parent directory ~/.azure/helm, not the required version subdirectory ~/.azure/helm/<version>.
• Failures occurred when ~/.azure/helm/<version> was missing, even if ~/.azure/helm already existed.
• It could appear to work when that specific <version> directory had already been created by a prior run.
• The fix now creates download_location (~/.azure/helm/<version>) directly before download.

[github-actions]

The git hooks are available for azure-cli and azure-cli-extensions repos. They could help you run required checks before creating the PR.

Please sync the latest code with latest dev branch (for azure-cli) or main branch (for azure-cli-extensions).
After that please run the following commands to enable git hooks:

pip install azdev --upgrade
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[github-actions]

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[Copilot]

Pull request overview

Adds ARM64-aware Helm client installation for the connectedk8s and k8s-extension Azure CLI extensions by detecting host architecture, constructing arch-specific Helm artifact paths, and ensuring the versioned download directory exists before saving/extracting the Helm archive.

Changes:

• Detects host CPU architecture (platform.machine()) and uses it to build Helm archive and install paths.
• Adds an ARM64 download flow that pulls Helm from the official Helm distribution when running on ARM64.
• Fixes a latent directory-creation issue by creating ~/.azure/helm/<version> before downloading the archive.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 8 comments.

File	Description
src/k8s-extension/azext_k8s_extension/custom.py	Adds arch detection, ARM64 Helm download path, and corrects download directory creation for Helm install flow.
src/connectedk8s/azext_connectedk8s/custom.py	Mirrors the same ARM64-aware Helm installation updates and directory handling fix for connectedk8s.