Add usage documentations

[aniruddha2000]

How to categorize this PR?

/kind enhancement

What this PR does / why we need it:

This PR introduce usage documentation, that includes workload identity, alb and cloudprofile.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Breaking changes:

[ske-prow]

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[dergeberl]

We should also add a note here that this is only possible if allowed in the admission webhook. We also should document (not in the usage.md, other extensions document such things in operations/deployment ) that this field can be configured.

gardener-extension-provider-stackit/charts/gardener-extension-admission-stackit/charts/runtime/values.yaml

Line 24 in 14cf9ff

#allowApplicationLoadBalancerController: false

[dergeberl]

We need to document here how to enable it in the controlplane not how SKE works.