feat: Add policy column to aws_efs_filesystems table (#14672)

#### Summary

resolves #14632

I'm looking for a way to reduce the duplicate implementations, for example, the following part is a way to get a service to resolve data for the table. It works well when a table relays on a single resolver. But if a table needs multiple resolver then might be a good way to do it. 

```go
	p := resource.Item.(types.FileSystemDescription)
	config := efs.DescribeFileSystemPolicyInput{
		FileSystemId: p.FileSystemId,
	}
	cl := meta.(*client.Client)
	svc := cl.Services(client.AWSServiceEfs).Efs
```

<!--
Explain what problem this PR addresses
-->

plugins/source/aws/resources/services/efs/filesystems.go

@@ -32,7 +32,12 @@ func Filesystems() *schema.Table {
 			{
 				Name:     "backup_policy_status",
 				Type:     arrow.BinaryTypes.String,
-				Resolver: ResolveEfsFilesystemBackupPolicyStatus,
+				Resolver: resolveEfsFilesystemBackupPolicyStatus,
+			},
+			{
+				Name:     "file_system_policy",
+				Type:     arrow.BinaryTypes.String,
+				Resolver: resolveEfsFilesystemPolicy,
 			},
 			{
 				Name:     "tags",
@@ -60,7 +65,7 @@ func fetchEfsFilesystems(ctx context.Context, meta schema.ClientMeta, parent *sc
 	return nil
 }
 
-func ResolveEfsFilesystemBackupPolicyStatus(ctx context.Context, meta schema.ClientMeta, resource *schema.Resource, c schema.Column) error {
+func resolveEfsFilesystemBackupPolicyStatus(ctx context.Context, meta schema.ClientMeta, resource *schema.Resource, c schema.Column) error {
 	p := resource.Item.(types.FileSystemDescription)
 	config := efs.DescribeBackupPolicyInput{
 		FileSystemId: p.FileSystemId,
@@ -82,3 +87,26 @@ func ResolveEfsFilesystemBackupPolicyStatus(ctx context.Context, meta schema.Cli
 
 	return resource.Set(c.Name, response.BackupPolicy.Status)
 }
+
+func resolveEfsFilesystemPolicy(ctx context.Context, meta schema.ClientMeta, resource *schema.Resource, c schema.Column) error {
+	p := resource.Item.(types.FileSystemDescription)
+	config := efs.DescribeFileSystemPolicyInput{
+		FileSystemId: p.FileSystemId,
+	}
+	cl := meta.(*client.Client)
+	svc := cl.Services(client.AWSServiceEfs).Efs
+	response, err := svc.DescribeFileSystemPolicy(ctx, &config, func(options *efs.Options) {
+		options.Region = cl.Region
+	})
+	if err != nil {
+		if cl.IsNotFoundError(err) {
+			return nil
+		}
+		return err
+	}
+	if response.Policy == nil {
+		return nil
+	}
+
+	return resource.Set(c.Name, response.Policy)
+}

plugins/source/aws/resources/services/efs/filesystems_mock_test.go

@@ -28,6 +28,11 @@ func buildEfsFilesystemsMock(t *testing.T, ctrl *gomock.Controller) client.Servi
 	m.EXPECT().DescribeBackupPolicy(gomock.Any(), gomock.Any(), gomock.Any()).Return(
 		&b, nil)
 
+	p := efs.DescribeFileSystemPolicyOutput{}
+	require.NoError(t, faker.FakeObject(&p))
+	m.EXPECT().DescribeFileSystemPolicy(gomock.Any(), gomock.Any(), gomock.Any()).Return(
+		&p, nil)
+
 	return client.Services{
 		Efs: m,
 	}

website/tables/aws/aws_efs_filesystems.md

@@ -16,6 +16,7 @@ The primary key for this table is **arn**.
 |region|`utf8`|
 |arn (PK)|`utf8`|
 |backup_policy_status|`utf8`|
+|file_system_policy|`utf8`|
 |tags|`json`|
 |creation_time|`timestamp[us, tz=UTC]`|
 |creation_token|`utf8`|