feat!: Upgrade min AWS provider and Terraform versions to 6.0 and 1.5.7 respectively

[kirylkaminski]

As stated in the closed (not fixed) issue: version 6.0.0 of the AWS provider has deprecated the name attribute on aws_region, and a warning is now shown on ${data.aws_region.current.name}.
This change uses region attribute instead of name to fix the deprecation warning.

Motivation and Context

Fixes #255

Important changes

Terraform AWS Lambda module version has been upgraded to 8.0.1, so previously managed IAM policy and attachment should be removed from the state file to avoid cycle errors:

terraform state rm "module.notify_slack.module.lambda.aws_iam_role_policy_attachment.additional_json[0]"
terraform state rm "module.notify_slack.module.lambda.aws_iam_policy.additional_json[0]"

Also, variable var.iam_policy_path has been removed.

[kirylkaminski]

@bryantbiggs could you please check? or someone else

[antonbabenko]

Please add the required changes to all versions.tf files - update the minimum Terraform version and AWS provider version.

[kirylkaminski]

@antonbabenko updated versions.tf with aws provider constraints, haven't found any mentions of specific terraform version constraint hight than >=1.0

[antonbabenko]

This PR is included in version 7.0.0 🎉

[github-actions]

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