add custom HTTP headers support for Schema Registry connections

[ymocode]

Enable per-cluster schemaRegistryHeaders configuration to pass custom
headers (e.g. X-Registry-GroupId) to the Schema Registry API. This
allows scoping Apicurio Registry's Confluent compatibility endpoint
to a specific artifact group.

Config: KAFKA_CLUSTERS_0_SCHEMAREGISTRYHEADERS_=

• Breaking change? No — new optional property, fully backward-compatible.

What changes did you make?

Added support for custom HTTP headers on Schema Registry WebClient connections, configured per cluster via schemaRegistryHeaders map.

This enables passing headers like X-Registry-GroupId to Apicurio Registry's Confluent compatibility API, scoping schema lookups to a specific artifact group.

Three files changed:

• ClustersProperties.Cluster — added Map<String, String> schemaRegistryHeaders
• WebClientConfigurator — added configureDefaultHeaders(Map<String, String>) method
• KafkaClusterFactory.schemaRegistryClient() — wired headers into WebClient builder

Configuration example:
KAFKA_CLUSTERS_0_SCHEMAREGISTRYHEADERS_X-Registry-GroupId=my.artifact.group

Is there anything you'd like reviewers to focus on?

The configureDefaultHeaders method appends to the existing defaultHeaders consumer chain — verify it doesn't conflict with configureBasicAuth which also uses defaultHeaders.

How Has This Been Tested?

• No need to
• Manually — verified headers are sent to Apicurio Registry and schemas scoped to the configured group are returned
• Unit checks
• Integration checks
• Covered by existing automation

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (e.g. ENVIRONMENT VARIABLES)
• My changes generate no new warnings (e.g. Sonar is happy)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged

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