[BUG] FG_R00252 should support arrays for condition values

[szesch]

Describe the bug
Some older terraform modules can create IAM conditions with an array of strings instead of a string. FG_R00252 only checks for strings so conditions with a value of type array will be flagged as a violation.

How you're running Regula
Regula v2.9.2 and Terraform v1.2.8 running against Terraform plan output.

$ regula version
v2.9.2, build b41673e, built with OPA v0.43.1

$ terraform -version
Terraform v1.2.8
on linux_amd64
+ provider registry.terraform.io/hashicorp/aws v4.40.0
+ provider registry.terraform.io/hashicorp/time v0.9.1

Operating System
Ubuntu 22.04

Steps to reproduce

terraform init
terraform plan -out plan
terraform show -json plan > plan.json
regula run --no-config --only FG_R00252 -t tf-plan plan.json

IaC Configuration

provider "aws" {
  region  = "us-east-2"
}

data "aws_caller_identity" "current" {}

data "aws_region" "current" {}

data "aws_partition" "current" {}

module "vpc" {
  source = "terraform-aws-modules/vpc/aws"

  name = "my-vpc"
  cidr = "10.0.0.0/16"

  azs             = ["eu-west-1a", "eu-west-1b", "eu-west-1c"]
  private_subnets = ["10.0.1.0/24", "10.0.2.0/24", "10.0.3.0/24"]
  public_subnets  = ["10.0.101.0/24", "10.0.102.0/24", "10.0.103.0/24"]

  enable_nat_gateway = false
  enable_vpn_gateway = false

  tags = {
    Terraform   = "true"
    Environment = "dev"
  }
}

module "test" {
  source  = "cloudposse/vpc-flow-logs-s3-bucket/aws"
  version = "0.18.0"

  namespace = "fugue"
  stage     = "test"
  name      = "test"

  vpc_id = module.vpc.vpc_id

  kms_policy_source_json = data.aws_iam_policy_document.test.json
}

data "aws_iam_policy_document" "test" {
  statement {
    actions = [
      "kms:Decrypt"
    ]

    resources = ["*"]

    principals {
      type        = "AWS"
      identifiers = ["*"]
    }
    condition {
      test     = "StringEquals"
      variable = "kms:CallerAccount"
      values   = [data.aws_caller_identity.current.account_id]
    }
    condition {
      test     = "StringEquals"
      variable = "kms:ViaService"
      values   = [format("s3.%s.amazonaws.com", data.aws_region.current.name)]
    }
  }

  statement {
    sid = "Enable IAM User Permissions"
    actions = [
      "kms:*",
    ]
    effect = "Allow"
    principals {
      type = "AWS"
      identifiers = [
        format(
          "arn:%s:iam::%s:root",
          data.aws_partition.current.partition,
          data.aws_caller_identity.current.account_id
        )
      ]
    }
    resources = ["*"]
  }
}

[szesch]

Addressed in #380