set kubelet's --provider-id flag

- What I did
I Added AWS specific systemd unit (aws-kubelet-providerid.service) and file (/usr/local/bin/aws-kubelet-providerid) for generating the AWS instance provider-id (then stored in the KUBELET_PROVIDERID env var), in order to pass it as the --provider-id argument to the kubelet service binary.
We needed to add such flag, and make it non-empty only on AWS, to make the node syncing (specifically backing instance detection) work via provider-id detection, to cover cases where the node hostname doesn't match the expected private-dns-name (e.g. when a custom DHCP Option Set with empty domain-name is used).

Should fix: https://bugzilla.redhat.com/show_bug.cgi?id=2084450
Reference to an upstream issue with context: kubernetes/cloud-provider-aws#384

- How to verify it
Try the reproduction steps available at: https://bugzilla.redhat.com/show_bug.cgi?id=2084450#c0 while launching a cluster with this MCO PR included.
Verify that the issue is not reproducible anymore.

templates/common/aws/files/usr-local-bin-aws-kubelet-providerid.yaml

@@ -0,0 +1,26 @@
+mode: 0755
+path: "/usr/local/bin/aws-kubelet-providerid"
+contents:
+  inline: |
+    #!/bin/bash
+    set -e -o pipefail
+
+    NODECONF=/etc/systemd/system/kubelet.service.d/20-aws-providerid.conf
+
+    if [ -e "${NODECONF}" ]; then
+        echo "Not replacing existing ${NODECONF}"
+        exit 0
+    fi
+
+    # Due to a potential mismatch between Hostname and PrivateDNSName with clusters that use custom DHCP Option Sets
+    # which can cause issues in cloud controller manager node syncing
+    # (see: https://github.com/kubernetes/cloud-provider-aws/issues/384),
+    # set KUBELET_PROVIDERID to be a fully qualified AWS instace provider id.
+    # This new variable is later used to populate the kubelet's `provider-id` flag, later set on the Node .spec
+    # and used by the cloud controller manager's node controller to retrieve the Node's backing instance.
+    # This is obtained by using afterburn service variables, in turn obtained from metadata retrival.
+    # See respective systemd unit metadata related afterburn doc: https://coreos.github.io/afterburn/usage/attributes/
+    cat > "${NODECONF}" <<EOF
+    [Service]
+    Environment="KUBELET_PROVIDERID=aws://${AFTERBURN_AWS_AVAILABILITY_ZONE}/${AFTERBURN_AWS_INSTANCE_ID}"
+    EOF

templates/common/aws/units/aws-kubelet-providerid.service.yaml

@@ -0,0 +1,23 @@
+name: aws-kubelet-providerid.service
+enabled: true
+contents: |
+  [Unit]
+  Description=Fetch kubelet provider id from AWS Metadata
+
+  # Run afterburn service for collect info from metadata server
+  # see: https://coreos.github.io/afterburn/usage/attributes/
+  Requires=afterburn.service
+  After=afterburn.service
+
+  # Wait for NetworkManager to report it's online
+  After=NetworkManager-wait-online.service
+  # Run before kubelet
+  Before=kubelet.service
+
+  [Service]
+  EnvironmentFile=/run/metadata/afterburn
+  ExecStart=/usr/local/bin/aws-kubelet-providerid
+  Type=oneshot
+
+  [Install]
+  WantedBy=network-online.target

templates/master/01-master-kubelet/_base/units/kubelet.service.yaml

@@ -40,6 +40,7 @@ contents: |
         --volume-plugin-dir=/etc/kubernetes/kubelet-plugins/volume/exec \
         {{cloudConfigFlag . }} \
         --hostname-override=${KUBELET_NODE_NAME} \
+        --provider-id=${KUBELET_PROVIDERID} \
         --register-with-taints=node-role.kubernetes.io/master=:NoSchedule \
         --pod-infra-container-image={{.Images.infraImageKey}} \
         --system-reserved=cpu=${SYSTEM_RESERVED_CPU},memory=${SYSTEM_RESERVED_MEMORY} \

templates/worker/01-worker-kubelet/_base/units/kubelet.service.yaml

@@ -40,6 +40,7 @@ contents: |
         --cloud-provider={{cloudProvider .}} \
         {{cloudConfigFlag . }} \
         --hostname-override=${KUBELET_NODE_NAME} \
+        --provider-id=${KUBELET_PROVIDERID} \
         --pod-infra-container-image={{.Images.infraImageKey}} \
         --system-reserved=cpu=${SYSTEM_RESERVED_CPU},memory=${SYSTEM_RESERVED_MEMORY} \
         --v=${KUBELET_LOG_LEVEL}