Allow override of CLUSTER_ARCH in container build

```suggestion
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 https://github.com/openshift/oadp-operator/pull/1478#discussion_r1705720436_
            