Switch docker_image to community.docker.docker_image

[andygrunwald]

Context

During execution, these messages are in the output:

task path: /my/path/.ansible/roles/mhutter.docker-systemd-service/tasks/main.yml:6
redirecting (type: modules) ansible.builtin.docker_image to community.docker.docker_image

task path: /my/path/.ansible/roles/mhutter.docker-systemd-service/tasks/install.yml:12
redirecting (type: modules) ansible.builtin.docker_image to community.docker.docker_image
redirecting (type: modules) ansible.builtin.docker_image to community.docker.docker_image

This PR is switching docker_image to community.docker.docker_image.

Checklist

• Keep pull requests small so they can be easily reviewed.