Fix: restore CommonName in ACME-issued certificates after lego v5 upgrade

[MartinWeindel]

How to categorize this PR?

/kind bug

What this PR does / why we need it:

Summary

Re-enables Common Name (CN) population in certificates issued via ACME after the lego v5 upgrade. lego v5 changed the default to omit CN; this PR opts back in via EnableCommonName: true on both ObtainRequest and ObtainForCSRRequest, restoring the pre-v5 behavior expected by existing consumers.

Changes

• pkg/shared/legobridge/certificate.go: set EnableCommonName: true in obtainForDomains and obtainForCSR.
• test/utils/pebble.go: set PromoteCommonName: true on both Pebble profiles so the local ACME CA emits a CN, mirroring the client-side opt-in (test-only).
• test/integration/controller/issuer/issuer_test.go: extend ACME tests to assert Subject.CommonName and DNSNames on the issued cert; add coverage for the CSR path (obtainForCSR) and for the "CommonName + extra
  DNSNames" combination. New helpers: buildCSR, parseCertFromSecret. getCertificate gains a variadic dnsNames parameter (backward-compatible).
• test/integration/controller/issuer/certificate_test.go: tighten the CA-path SAN test with a Subject.CommonName assertion.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Release note:

ACME-issued certificates now include the correct Subject Common Name again. The recent lego v5 upgrade had silently dropped the CN from issued certificates, breaking consumers that pin to or parse `Subject.CommonName`. The CN is now populated from `spec.commonName` (or the first DNS name when CN is unset and ≤64 characters).

[MartinWeindel]

/cc @marc1404

[marc1404]

/lgtm
/approve

[gardener-prow]

LGTM label has been added.

Details

Git tree hash: be145ceb938df0d52842402ef2b05627d1517b53

[gardener-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: marc1404

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[MartinWeindel]

/cherry-pick release-v0.24

[gardener-ci-robot]

@MartinWeindel: new pull request created: #745

Details

In response to this:

/cherry-pick release-v0.24

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