Added cloud-init KB and examples

cloud-init/base.yaml

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+#cloud-config
+
+# Sources:
+# - https://github.com/trajano/terraform-docker-swarm-aws/blob/master/common.cloud-config
+
+# Upgrade the instance
+# Deactivated as this could take a long time if the image is old
+# https://cloudinit.readthedocs.io/en/latest/topics/modules.html#package-update-upgrade-install
+# https://cloudinit.readthedocs.io/en/latest/topics/examples.html#run-apt-or-yum-upgrade
+package_upgrade: false
+package_reboot_if_required: false
+
+# Install required packages
+# This will always update the list of packages, regardless of package_update's value.
+# https://cloudinit.readthedocs.io/en/latest/topics/modules.html#package-update-upgrade-install
+# https://cloudinit.readthedocs.io/en/latest/topics/examples.html#install-arbitrary-packages
+packages:
+  - jq
+  - nc
+  - traceroute
+  - unzip

cloud-init/docker.yum.yaml

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+#cloud-config
+
+# Sources:
+# - https://github.com/trajano/terraform-docker-swarm-aws/blob/master/common.cloud-config
+
+# Add the Docker repository
+# https://cloudinit.readthedocs.io/en/latest/topics/modules.html#yum-add-repo
+# https://cloudinit.readthedocs.io/en/latest/topics/examples.html#adding-a-yum-repository
+#
+# Got from the official installation guide at
+# https://docs.docker.com/engine/install/rhel/#install-using-the-repository :
+#   yum install -y yum-utils && \
+#   yum-config-manager --add-repo \
+#     https://download.docker.com/linux/rhel/docker-ce.repo && \
+#   cat /etc/yum.repos.d/docker-ce.repo
+yum_repos:
+  docker-ce:
+    name: Docker CE Stable - $basearch
+    enabled: true
+    baseurl: https://download.docker.com/linux/rhel/$releasever/$basearch/stable
+    priority: 1
+    gpgcheck: true
+    gpgkey: https://download.docker.com/linux/rhel/gpg
+
+# Install required packages
+# This will always update the list of packages, regardless of package_update's value.
+# https://cloudinit.readthedocs.io/en/latest/topics/modules.html#package-update-upgrade-install
+# https://cloudinit.readthedocs.io/en/latest/topics/examples.html#install-arbitrary-packages
+#
+# docker-ce already depends on docker-ce-cli and containerd.io
+packages:
+  - docker-ce
+
+# Enable and start the service after installation
+runcmd:
+  - systemctl daemon-reload
+  - systemctl enable --now docker.service