[Containerapp]: az containerapp arc: Enable setup custom core dns for Openshift

[anandgmenon]

… Openshift on Arc

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[azure-client-tools-bot-prd]

Hi @anandgmenon,
Please write the description of changes which can be perceived by customers into HISTORY.rst.
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[Copilot]

Pull Request Overview

This PR adds support for custom CoreDNS setup for OpenShift clusters alongside the existing AKS support.

• Adds OpenShift-specific constants and logic to create and patch CoreDNS resources.
• Introduces new functions in _arc_utils.py for managing deployments, config maps, and DNS operator configurations on OpenShift.
• Updates CLI parameter definitions to include OpenShift as a supported distro.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/containerapp/azext_containerapp/custom.py	Adds OpenShift branch in setup_core_dns and related logging/error handling.
src/containerapp/azext_containerapp/_params.py	Updates CLI argument to include OpenShift distro with a minor typo in the help text.
src/containerapp/azext_containerapp/_constants.py	Introduces new constants for OpenShift support.
src/containerapp/azext_containerapp/_arc_utils.py	Adds multiple helper functions for creating/updating resources and patching DNS operator for OpenShift.

Comments suppressed due to low confidence (1)

src/containerapp/azext_containerapp/_arc_utils.py:637

• [nitpick] The error message appears counterintuitive; consider rephrasing it to indicate that the required key is missing (e.g., "'k4apps-default.io.server' key not found in the coredns-custom ConfigMap in kube-system namespace.").

raise ValidationError("'k4apps-default.io.server' key found in the coredns-custom ConfigMap in kube-system namespace.")

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[github-actions]

Hi @anandgmenon

Release Suggestions

Module: containerapp

• Please log updates into to src/containerapp/HISTORY.rst
• Update VERSION to 1.2.0b2 in src/containerapp/setup.py

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