Add docker role for making sure Docker is installed

Add a docker role for making sure Docker is installed from the Docker
repositories.
Take the role from the ccchh-ansible repo, provide attribution in the
README and add the relevant license in a new licenses directory.
Modify the role by removing the distribution check and adjusting the
task names to be in line with other task names in this repo.

playbooks/roles/docker/README.md

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+# Role `docker`
+
+Makes sure Docker Engine and other related packages are installed from the Docker repos on the specified hosts.
+For details see: [`tasks/main/02_docker_install.yaml`](./tasks/main/02_docker_install.yaml).
+
+## Required Arguments
+
+None.
+
+## Updates
+
+This role doesn't handle updates.
+However it uses the system package manager for installing Docker Engine and the other related packages, so when you're making sure the system packages are up-to-date, you're handling updates for the packages installed by this role as well.
+
+## `hosts`
+
+The `hosts` for this role need to be the machines for which you want to make sure Docker Engine and other related packages are installed from the Docker repos.
+
+## Links & Resources
+
+- <https://docs.docker.com/engine/install/debian/>

playbooks/roles/docker/tasks/main.yaml

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+- name: Ensure the Docker repo is setup
+  ansible.builtin.import_tasks:
+    file: main/01_repo_setup.yaml
+
+- name: Ensure Docker Engine and other related packages are installed
+  ansible.builtin.import_tasks:
+    file: main/02_docker_install.yaml

playbooks/roles/docker/tasks/main/01_repo_setup.yaml

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+- name: Ensure Dockers GPG key is added
+  ansible.builtin.get_url:
+    url: https://download.docker.com/linux/debian/gpg
+    dest: /etc/apt/trusted.gpg.d/docker.asc
+    mode: "0644"
+    owner: root
+    group: root
+  become: true
+
+- name: Ensure Dockers APT repository is added
+  ansible.builtin.apt_repository:
+    repo: "deb [arch=amd64 signed-by=/etc/apt/trusted.gpg.d/docker.asc] https://download.docker.com/linux/debian {{ ansible_distribution_release }} stable"
+    filename: docker
+    state: present
+  become: true

playbooks/roles/docker/tasks/main/02_docker_install.yaml

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+- name: Ensure Docker Engine and other related packages are installed
+  ansible.builtin.apt:
+    name:
+      - docker-ce
+      - docker-ce-cli
+      - containerd.io
+      - docker-buildx-plugin
+      - docker-compose-plugin
+    state: present
+    update_cache: true
+  become: true