admission/initializer: getting rid of constructor

[sttts]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

Remove pointless boilerplate.

// TODO: switch these parameters to use the builder pattern or just make them
//       all public, this construction method is pointless boilerplate.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[sttts]

Agreed with @deads2k to go with constructors, also in generic controlplane follow-up.

[cici37]

/triage accepted