Cleanup CloudProfile docker migration and Add Validation MachineImageVersion CRI

[acumino]

How to categorize this PR?

/area control-plane /kind cleanup

What this PR does / why we need it: This PR adds validation for the CloudProfile MachineImageVersion CRI field. Now spec.machineImages[].versions[].cri in CloudProfile can't be set to nil. Also docker is added by default in cri. This defaulting of docker in cri can be removed after completion of https://github.com/gardener/gardener/issues/4673.

Which issue(s) this PR fixes: Fixes https://github.com/gardener/gardener/issues/6375

Special notes for your reviewer:

Release note:

NONE

[acumino]

/test pull-gardener-e2e-kind

[timebertt]

/assign

[gardener-prow[bot]]

@acumino: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-gardener-apidiff	90e7a1980c2d190898d52e0d77be8fd835fded5c	link	false	/test pull-gardener-apidiff

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[gardener-prow[bot]]

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This pull-request has been approved by: timebertt

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