Add support for aws_cloudwatch_log_group log_group_class

[jfreeland]

Is your request related to a new offering from AWS?

Is this functionality available in the AWS provider for Terraform? See CHANGELOG.md, too.

• Yes ✅: https://github.com/hashicorp/terraform-provider-aws/blob/main/CHANGELOG.md#5310-december-15-2023

Is your request related to a problem? Please describe.

No.

Describe the solution you'd like.

I'd like to be able to specify flow_log_group_class as INFREQUENT_ACCESS.

Describe alternatives you've considered.

Submitting a PR.

Additional context

I'm busy and doing other stuff but wanted to jot down this note.