Switch controller-manager to logr (5)

[timebertt]

How to categorize this PR?

/area logging dev-productivity
/kind enhancement

What this PR does / why we need it:

Continuation of #5488
Migrate controller-manager shoot controller to logr.
This was the last one in controller-manager, meaning it is fully migrated now.

Which issue(s) this PR fixes:
Part of #4251

Special notes for your reviewer:

We have to keep instantiating logger.Logger in controller-manager for now, as there are a few minor usages in helper funcs shared with gardenlet.
We can drop this, once they have been switched as well.

Release note:

NONE

[gardener-prow]

@timebertt: 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	242d705	link	false	/test pull-gardener-apidiff

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[rfranzke]

/assign

[rfranzke]

/lgtm
/approve

[gardener-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: rfranzke

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