feat: Support VPC flow log cloudwatch log group class

[magreenbaum]

Description

Add support for VPC flow log cloudwatch log group class. https://github.com/hashicorp/terraform-provider-aws/pull/34679

Motivation and Context

Closes: https://github.com/terraform-aws-modules/terraform-aws-vpc/issues/1050

Breaking Changes

No.

How Has This Been Tested?

• [x] I have updated at least one of the examples/* to demonstrate and validate my change(s)
• [x] I have tested and validated these changes using one or more of the provided examples/* projects
• [x] I have executed pre-commit run -a on my pull request

[antonbabenko]

This PR is included in version 5.6.0 :tada:

[github-actions[bot]]

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