[ST]: Update CustomCaST to check all certificates

[katheris]

Related problem

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Suggested solution

In CustomCaST in many of the tests (e.g. https://github.com/strimzi/strimzi-kafka-operator/blob/main/systemtest/src/test/java/io/strimzi/systemtest/security/custom/CustomCaST.java#L306) we only check the certificates for a single Kafka node. We should check all the certificates, which once #10967 is merged will be stored in separate Secrets.

Alternatives

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Additional context

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[ppatierno]

Triaged on 23.1.2025: we should update the STs as proposed by Kate.