Support AWS MSK Authentication

[nonamef]

Is your feature request related to a problem? Please describe.

Currently using fluent with AWS MSK as unauthenticated with security groups to control access. Want to enable AWS IAM assume role for cross account access.

Describe the solution you'd like

Same setup as fluent-plugin-s3 for assume_role_credentials would be good.
e.g https://github.com/fluent/fluent-plugin-s3/blob/master/docs/credentials.md

Describe alternatives you've considered

Only alternative is to continue as unauthenticated.

Additional context

No response

[github-actions]

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[raytung]

Hey @nonamef We have added AWS IAM auth support with access keys and secret keys. Unfortunately, since the ruby-kafka gem is deprecated, they are not adding support for assume roles. Looks like librdkafka is also not supporting AWS IAM auth so our hands are a bit tied on this one.