data: add approve-csr service to approve CSRs until bootstrap is complete

PR for cluster-machine-approver [1] is taking over the approval of CSRs for client certificates for Machines that end up
as Nodes in Openshift clusters.

But during bootstrapping, cluster-machine-approver is not available and therefore, this service is required to approve CSRs until
we have successfully bootstrapped the control plane, after which cluster-machine-approver or users take over the role of approving any new CSRs.

Currently, all CSRs are automatically approved without any condition, this PR scopes it to only during bootstrapping phase, securing the endpoint for later use.

[1]: openshift/cluster-machine-approver#26

Author: abhinavdahiya

data/data/bootstrap/files/usr/local/bin/approve-csr.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+
+KUBECONFIG="${1}"
+
+echo "Approving all CSR requests until bootstrapping is complete..."
+while [ ! -f /opt/openshift/bootkube.done ]
+do
+    oc --config="$KUBECONFIG" get csr --no-headers | grep Pending | \
+        awk '{print $1}' | \
+        xargs --no-run-if-empty oc --config="$KUBECONFIG" adm certificate approve
+	sleep 20
+done

data/data/bootstrap/systemd/units/approve-csr.service

@@ -0,0 +1,13 @@
+[Unit]
+Description=Approve CSRs during bootstrap phase
+Wants=bootkube.service
+After=bootkube.service
+
+[Service]
+ExecStart=/usr/local/bin/approve-csr.sh /opt/openshift/auth/kubeconfig
+
+Restart=on-failure
+RestartSec=5s
+
+[Install]
+WantedBy=multi-user.target

pkg/asset/ignition/bootstrap/bootstrap.go

@@ -248,6 +248,7 @@ func (a *Bootstrap) addSystemdUnits(uri string, templateData *bootstrapTemplateD
 		"kubelet.service":                 {},
 		"chown-gatewayd-key.service":      {},
 		"systemd-journal-gatewayd.socket": {},
+		"approve-csr.service":             {},
 	}
 
 	directory, err := data.Assets.Open(uri)