CSI compatibility mode

[ftl]

How to categorize this PR?

/kind enhancement

What this PR does / why we need it:
This change allows to deploy two separate instances of the STACKIT CSI driver, on in "normal" mode, and the second one in "compatibility" mode. This is part of the migration from cinder to the STACKIT CSI driver.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:
This change requires the enhancement stackitcloud/cloud-provider-stackit#161 to be available in the cloud-provider-stackit CSI driver plugin.

Breaking changes:

[ske-prow]

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[ftl]

/test pull-gardener-extension-provider-stackit-verify

[ske-prow]

@ftl: 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-extension-provider-stackit-verify	6f82793	link	true	/test pull-gardener-extension-provider-stackit-verify

Full PR test history. Your PR dashboard. Command help for this repository.
Please help us cut down on flakes by linking this test failure to an open flake report or filing a new flake report if you can't find an existing one. Also see the gardener testing guideline for how to avoid and hunt flakes.

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