[metrics]: support new namespace ApplicationSignals

[jianpingzhangBill]

AWS Applicaiton Signals Metrics fail to scrape.

Example:
Here is my terraform code to create an exporter with query AppSignals

resource "helm_release" "cloudwatch_exporter" {

  name       = "cloudwatch-exporter"
  repository = "https://prometheus-community.github.io/helm-charts"
  chart      = "prometheus-cloudwatch-exporter"
  version    = "0.25.3"
  namespace  = data.aws_ssm_parameter.name_space.value
  wait       = "false"
  values = [<<-EOF
serviceMonitor:
  enabled: true
  timeout: 10s
# resources: 
#   limits:
#     cpu: 100m
#     memory: 128Mi
#   requests:
#     cpu: 100m
#     memory: 128Mi
serviceAccount:
  create: true
  name:
  # annotations:
  # Will add the provided map to the annotations for the created serviceAccount
  # e.g.
  annotations:
    eks.amazonaws.com/role-arn: arn:aws:iam::${local.account_id}:role/prom-cloudwatch-exporter-oidc
    eks.amazonaws.com/sts-regional-endpoints: "true"

  automountServiceAccountToken: true


config: |-
  delay_seconds: 30
  period_seconds: 30
  debug: true
  metrics:
  # SELECT AVG(Latency) FROM AppSignals GROUP BY Operation, RemoteOperation, "HostedIn.K8s.Namespace",  Service, RemoteService
  - aws_namespace: AppSignals
    aws_metric_name: Latency
    aws_dimensions: [Operation, RemoteOperation, "HostedIn.K8s.Namespace",  Service, RemoteService]
    aws_statistics: [Average]

  - aws_dimensions:
    - CacheNodeId
    - CacheClusterId
    aws_metric_name: CPUUtilization
    aws_namespace: AWS/ElastiCache
    aws_statistics:
    - Average
  - aws_dimensions:
    - CacheNodeId
    - CacheClusterId
    aws_metric_name: CPUCreditBalance
    aws_namespace: AWS/ElastiCache
    aws_statistics:
    - Average
  - aws_dimensions:
    - CacheNodeId
    - CacheClusterId
    aws_metric_name: FreeableMemory
    aws_namespace: AWS/ElastiCache
    aws_statistics:
    - Average
  
  EOF
  
  ]
  depends_on = [
    shell_script.init
  ]
}


resource "aws_iam_policy" "cloudwatch_exporter" {
  name   = "prom-cloudwatch-exporter-oidc-policy"
  policy = <<EOF
{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Action": [
                "kms:DescribeKey",
                "kms:GenerateDataKey*",
                "kms:Decrypt",
                "kms:Encrypt",
                "kms:ReEncrypt*"
            ],
            "Effect": "Allow",
            "Resource": "*"
        },
        {
            "Action": [
                "tag:GetResources",
                "cloudwatch:GetMetricData",
                "cloudwatch:GetMetricStatistics",
                "cloudwatch:ListMetrics",
                "apigateway:GET",
                "aps:ListWorkspaces",
                "autoscaling:DescribeAutoScalingGroups",
                "dms:DescribeReplicationInstances",
                "dms:DescribeReplicationTasks",
                "ec2:DescribeTransitGatewayAttachments",
                "ec2:DescribeSpotFleetRequests",
                "shield:ListProtections",
                "storagegateway:ListGateways",
                "storagegateway:ListTagsForResource"
            ],
            "Effect": "Allow",
            "Resource": "*"
        }
    ]
}
EOF
}


resource "aws_iam_role" "cloudwatch_exporter_service_role" {
  name = "prom-cloudwatch-exporter-oidc"

  assume_role_policy = jsonencode({
    Version = "2012-10-17"
    Statement = [
      {
        Action = "sts:AssumeRoleWithWebIdentity"
        Effect = "Allow"
        Sid    = ""
        Principal = {
          Federated = "${data.terraform_remote_state.eks.outputs.aws_iam_openid_connect_provider_arn}"
        }
        Condition = {
          StringEquals = {
            "${data.terraform_remote_state.eks.outputs.aws_iam_openid_connect_provider_extract_from_arn}:sub": "system:serviceaccount:${data.aws_ssm_parameter.name_space.value}:cloudwatch-exporter-prometheus-cloudwatch-exporter"
          }
        }
      }
    ]
  })
}

resource "aws_iam_role_policy_attachment" "extra_policy" {
  policy_arn = aws_iam_policy.cloudwatch_exporter.arn
  role       = aws_iam_role.cloudwatch_exporter_service_role.name
}