[Doc] Replaced managed_policy_arns with aws_iam_role_policy_attachment in guides (#4737)

## Changes
`managed_policy_arns` are deprecated -
hashicorp/terraform-provider-aws#39771

## Tests
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- [x] relevant change in `docs/` folder

Author: nkvuong

NEXT_CHANGELOG.md

@@ -14,6 +14,8 @@
 
 ### Documentation
 
+ * Replaced `managed_policy_arns` with `aws_iam_role_policy_attachment` in AWS guides ([#4737](https://github.com/databricks/terraform-provider-databricks/pull/4737)).
+
 ### Exporter
 
 ### Internal Changes

docs/data-sources/aws_unity_catalog_assume_role_policy.md

@@ -33,7 +33,11 @@ resource "aws_iam_policy" "unity_metastore" {
 resource "aws_iam_role" "metastore_data_access" {
   name                = "${var.prefix}-uc-access"
   assume_role_policy  = data.databricks_aws_unity_catalog_assume_role_policy.this.json
-  managed_policy_arns = [aws_iam_policy.unity_metastore.arn]
+}
+
+resource "aws_iam_role_policy_attachment" "metastore_data_access" {
+  role       = aws_iam_role.metastore_data_access.name
+  policy_arn = aws_iam_policy.unity_metastore.arn
 }
 ```
 

docs/data-sources/aws_unity_catalog_policy.md

@@ -33,7 +33,11 @@ resource "aws_iam_policy" "unity_metastore" {
 resource "aws_iam_role" "metastore_data_access" {
   name                = "${var.prefix}-uc-access"
   assume_role_policy  = data.databricks_aws_unity_catalog_assume_role_policy.this.json
-  managed_policy_arns = [aws_iam_policy.unity_metastore.arn]
+}
+
+resource "aws_iam_role_policy_attachment" "metastore_data_access" {
+  role       = aws_iam_role.metastore_data_access.name
+  policy_arn = aws_iam_policy.unity_metastore.arn
 }
 ```
 

docs/guides/unity-catalog.md

@@ -264,11 +264,15 @@ resource "aws_iam_policy" "external_data_access" {
 resource "aws_iam_role" "external_data_access" {
   name                = local.uc_iam_role
   assume_role_policy  = data.databricks_aws_unity_catalog_assume_role_policy.this.json
-  managed_policy_arns = [aws_iam_policy.external_data_access.arn]
   tags = merge(var.tags, {
     Name = "${local.prefix}-unity-catalog external access IAM role"
   })
 }
+
+resource "aws_iam_role_policy_attachment" "external_data_access" {
+  role       = aws_iam_role.external_data_access.name
+  policy_arn = aws_iam_policy.external_data_access.arn
+}
 ```
 
 Then we can create the [databricks_external_location](../resources/external_location.md) in Unity Catalog.