KAFKA-18754: Allow PlainSaslServer to pass client info through the negotiated properties.

[bachmanity1]

In our organization, we use a custom Kafka authorizer that makes decisions based on client roles assigned by our IAM server. We've also implemented a custom PlainServerCallbackHandler that authenticates clients using their username and password through the IAM server. The IAM server also returns client info, such as assigned roles, but we're facing an issue—PlainSaslServer can only pass the authorizationID to the authorizer, meaning the client info is lost. To solve this, we want to extend PlainSaslServer so it can pass client info through the negotiated properties.

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)

[bachmanity1]

Hi @rajinisivaram, @ijuma, @gongxuanzhang, could you please take a look? (Tagging based on the git history of the modified files.)