out_cloudwatch_logs: fix disabled auto_create_group

[sjoerdsmink]

Fixes #8949

Since release 3.0.7 auto_create_group couldn't be set to Off anymore. That was a breaking change.

I didn't see any reason why log_group_class_type and log_group_class should be set, as they're not used when [auto_]create_group is off.

Please review @PettitWesley @edsiper

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[cschp]

hoping to see this tested and merged soon

[edsiper]

LGTM