OSDOCS-19006: Add Azure procedure for migrating x86 control plane to arm64

[bshaw7]

OSDOCS-19006

Adds documentation for migrating the control plane from x86 to arm64 architecture on Microsoft Azure, following the same pattern as the existing AWS and GCP procedures.

Unlike AWS (which has pre-published ARM AMIs), Azure requires manually creating a shared image gallery image from the arm64 RHCOS VHD before updating the control plane machine set.

Parent feature: OCPSTRAT-3088 — Azure Control Plane migration from X86 to ARM

Changes

• New module: modules/migrating-from-x86-to-arm-cp-azure.adoc — step-by-step procedure for Azure
• Updated assembly: updating/updating_a_cluster/migrating-to-multi-payload.adoc — added include and additional resources for Azure

Procedure steps (Azure-specific)

1. Set Azure resource variables (INFRA_ID, RESOURCE_GROUP, etc.)
2. Get arm64 RHCOS VHD URL from coreos-bootimages configmap
3. Copy VHD to cluster storage account (~17 GB, ~5 min)
4. Create arm64 image definition in shared image gallery
5. Create gallery image version from VHD
6. Patch control plane machine set with arm64 image and ARM VM size

Testing

Procedure verified on OCP 4.20.19 IPI cluster in eastus region (SUPPORTEX-30140).

• 3 masters migrated from Standard_D8s_v3 (x86) to Standard_D8ps_v6 (arm64)
• CPMS rollout completed in ~55 minutes
• All 34 cluster operators Available/Not Degraded after migration

Related

• Jira: OSDOCS-19006
• Parent: OCPSTRAT-3088
• Support case: SUPPORTEX-30140
• Existing AWS procedure: modules/migrating-from-x86-to-arm-cp.adoc
• Existing GCP procedure: modules/multiarch-migrating-cp-infra-gcp.adoc