[Bug]: Config provider alias conflict in Kafka config

[fvaleri]

Bug Description

When a user defines a Kafka configuration in .spec.kafka.config that includes a config provider alias with the same name as one automatically created by the operator, the user's alias takes precedence. This occurs because the user's configuration is written after the operator's in the final Kafka config file, effectively overriding the operator-defined alias. As a result, the Kafka configuration may be invalid or behave unexpectedly.

Steps to reproduce

In the following example, a bad user configuration causes all Kafka nodes to crash loop:

$ kubectl get k my-cluster -o yaml | yq '.spec.kafka.config'
...
config.providers: strimzienv
config.providers.strimzienv.class: org.apache.kafka.common.config.provider.EnvVarConfigProvider
config.providers.strimzienv.param.allowlist.pattern: test.*

$ kubectl exec my-cluster-broker-0 -- cat /tmp/strimzi.properties
##########
# Config providers
##########
# Configuration providers configured by the user and by Strimzi
config.providers=strimzienv,strimzienv,strimzifile,strimzidir
config.providers.strimzienv.class=org.apache.kafka.common.config.provider.EnvVarConfigProvider
config.providers.strimzienv.param.allowlist.pattern=.*
config.providers.strimzifile.class=org.apache.kafka.common.config.provider.FileConfigProvider
config.providers.strimzifile.param.allowed.paths=/opt/kafka
config.providers.strimzidir.class=org.apache.kafka.common.config.provider.DirectoryConfigProvider
config.providers.strimzidir.param.allowed.paths=/opt/kafka

##########
# User provided configuration
##########
config.providers.strimzienv.class=org.apache.kafka.common.config.provider.EnvVarConfigProvider
config.providers.strimzienv.param.allowlist.pattern=test.*

Expected behavior

Config providers is a critical configuration for the operator, so any conflicting user configuration should throw an InvalidConfiguration exception.

Strimzi version

main

Kubernetes version

1.32

Installation method

No response

Infrastructure

No response

Configuration files and logs

No response

Additional context

No response