Fix RabbitMQ Scaler Passwordless TLS Authentication

[HsiuChuanHsu]

Changes

Added support for passwordless authentication mode through a new usePasswordless parameter:

• Added UsePasswordless field to rabbitMQMetadata struct
• Added check to require username when usePasswordless=true in Validate() method
• Added condition to handle passwordless mode in URI parsing in NewRabbitMQScaler()
• Properly sets Basic Auth header with username only in getQueueInfoViaHTTP()

Checklist

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• Tests have been added
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Fixes #6840

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[rickbrouwer]

Wouldn't it be better to create an option in TypedConfig that allows an empty value to be parsed? Is that what you want with this PR? wdyt?

[HsiuChuanHsu]

Agree! It would be better to set a option in TypedConfig. Here is the new update summary:

• Add allowEmpty tag support in typed_config (new constant, Params field, and parsing logic)
• Mark rabbitmq password field as allowEmpty