Switch to for_each for log forwarding resources

In case `var.cloudwatch_log_groups` changes somewhere in the middle of the list, all resources indexed since that position must be recreated. This can be remedied by switching to `for_each` instead of `count`

logs_monitoring_cloudwatch_log.tf

@@ -1,17 +1,17 @@
 resource "aws_cloudwatch_log_subscription_filter" "test_lambdafunction_logfilter" {
-  count           = length(var.cloudwatch_log_groups)
-  name            = "${var.cloudwatch_log_groups[count.index]}-filter"
-  log_group_name  = var.cloudwatch_log_groups[count.index]
+  for_each        = { for lg in var.cloudwatch_log_groups : lg => lg }
+  name            = "${each.value}-filter"
+  log_group_name  = each.value
   filter_pattern  = ""
   destination_arn = aws_cloudformation_stack.datadog-forwarder.outputs.DatadogForwarderArn
   distribution    = "Random"
 }
 
 resource "aws_lambda_permission" "allow_cloudwatch_logs_to_call_dd_lambda_handler" {
-  count         = length(var.cloudwatch_log_groups)
-  statement_id  = "${substr(replace(var.cloudwatch_log_groups[count.index], "/", "_"), 0, 67)}-AllowExecutionFromCloudWatchLogs"
+  for_each      = { for lg in var.cloudwatch_log_groups : lg => lg }
+  statement_id  = "${substr(replace(each.value, "/", "_"), 0, 67)}-AllowExecutionFromCloudWatchLogs"
   action        = "lambda:InvokeFunction"
   function_name = aws_cloudformation_stack.datadog-forwarder.outputs.DatadogForwarderArn
   principal     = "logs.${var.aws_region}.amazonaws.com"
-  source_arn    = "arn:aws:logs:${var.aws_region}:${var.aws_account_id}:log-group:${var.cloudwatch_log_groups[count.index]}:*"
+  source_arn    = "arn:aws:logs:${var.aws_region}:${var.aws_account_id}:log-group:${each.value}:*"
 }