Allow override of CLUSTER_ARCH in container build

[kaovilai]

CLUSTER_OS ?= $(shell $(OC_CLI) get node -o jsonpath='{.items[0].status.nodeInfo.operatingSystem}' 2> /dev/null)
CLUSTER_ARCH ?= $(shell $(OC_CLI) get node -o jsonpath='{.items[0].status.nodeInfo.architecture}' 2> /dev/null)

Originally posted by @kaovilai in #1478 (comment)

[openshift-bot]

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/lifecycle stale

[kaovilai]

/remove-lifecycle stale