Fix iam files with snakecase back to camelcase

[modular-magician]

In previous PR GoogleCloudPlatform/magic-modules#5594, it turns asset name from camel case to snake case, which is incorrect for a few resources including private ca pool. This PR reverts that and add a handwritten file for servicemanagent service iam.

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Derived from GoogleCloudPlatform/magic-modules#5605