Consider removing the installation and enablement of the docker unit

[ialidzhikov]

How to categorize this issue?

/area os
/kind enhancement
/os ubuntu

What would you like to be added:
Right now, os-ubuntu as part of the init OperatingSystemConfig has:

gardener-extension-os-ubuntu/pkg/controller/operatingsystemconfig/actuator.go

Lines 81 to 82 in 20b2b22

	until apt-get update -qq && apt-get install --no-upgrade -qqy containerd runc docker.io socat nfs-common logrotate jq policykit-1; do sleep 1; done
	ln -s /usr/bin/docker /bin/docker

gardener-extension-os-ubuntu/pkg/controller/operatingsystemconfig/actuator.go

Line 100 in 20b2b22

systemctl enable docker && systemctl restart docker

docker is being installed via apt-get, then it is being enabled and restarted.

Similar to the reasoning in gardener/gardener-extension-os-gardenlinux#221:

From Gardener side, the docker binary is no longer used/required on a Shoot Node: gardener/gardener#4673.

As Gardener no longer requires docker, we should no longer install and enable it due to security reasons.

Pay attention that the change might be breaking for end users and it has to be coordinated with them somehow - via announcement and/or feature gate. See gardener/gardener-extension-os-gardenlinux#221 (comment)
The breaking part would be that end user might want to rely on docker to be installed and enabled for usage outside of Kubernetes (not recommended).

Why is this needed:

• Faster machine boot, we would no longer install docker on the fly
• Having docker installed and enabled is a security risk. See how docker on the OS was part of security attack (after attacker "escaped" the container) - SAPwned: SAP AI vulnerabilities expose customers’ cloud environments and private AI artifacts