CAMEL-23351: camel-oaipmh: Add custom HTTP Headers

[claudio4j]

Description

https://issues.apache.org/jira/browse/CAMEL-23351

Target

• I checked that the commit is targeting the correct branch (Camel 4 uses the main branch)

Tracking

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Apache Camel coding standards and style

• I checked that each commit in the pull request has a meaningful subject line and body.

• I have run mvn clean install -DskipTests locally from root folder and I have committed all auto-generated changes.

[github-actions]

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[github-actions]

🧪 CI tested the following changed modules:

• catalog/camel-catalog
• components/camel-oaipmh
• docs
• dsl/camel-endpointdsl

All tested modules (10 modules)

• Camel :: Catalog :: Camel Catalog
• Camel :: Endpoint DSL
• Camel :: JBang :: MCP
• Camel :: JBang :: Plugin :: Route Parser
• Camel :: JBang :: Plugin :: TUI
• Camel :: JBang :: Plugin :: Validate
• Camel :: Launcher :: Container
• Camel :: OAIPMH
• Camel :: YAML DSL :: Validator
• Camel :: YAML DSL :: Validator Maven Plugin

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