Support custom token payload

[tuteng]

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Motivation

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Modifications

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customPayload:
    superToken: "\\\"role\\\":[\\\"admin\\\"]|\\\"role2\\\":\\\"admin2\\\""
    nonSuperToken: "\\\"role\\\":[\\\"admin\\\",{{identity.entity.aliases.MOUNT_ACCESSOR.metadata.role_name}}]"

Verifying this change

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This change is a trivial rework / code cleanup without any test coverage.

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This change added tests and can be verified as follows:

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• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

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[github-actions]

@tuteng:Thanks for your contribution. For this PR, do we need to update docs?
(The PR template contains info about doc, which helps others know more about the changes. Can you provide doc-related info in this and future PR descriptions? Thanks)