data-source/aws_ecr_image: Use AWS Go SDK provided conversion functio…

…ns to prevent panics

Reference: #8403

Output from acceptance testing:

```
--- PASS: TestAccAWSEcrDataSource_ecrImage (14.26s)
--- PASS: TestAccAWSEcrDataSource_ecrRepository (17.23s)
```

aws/data_source_aws_ecr_image.go

@@ -99,18 +99,21 @@ func dataSourceAwsEcrImageRead(d *schema.ResourceData, meta interface{}) error {
 	image := imageDetails[0]
 
 	d.SetId(time.Now().UTC().String())
-	if err = d.Set("registry_id", *image.RegistryId); err != nil {
+	if err = d.Set("registry_id", aws.StringValue(image.RegistryId)); err != nil {
 		return fmt.Errorf("failed to set registry_id: %s", err)
 	}
-	if err = d.Set("image_digest", *image.ImageDigest); err != nil {
+	if err = d.Set("image_digest", aws.StringValue(image.ImageDigest)); err != nil {
 		return fmt.Errorf("failed to set image_digest: %s", err)
 	}
 	if err = d.Set("image_pushed_at", image.ImagePushedAt.Unix()); err != nil {
 		return fmt.Errorf("failed to set image_pushed_at: %s", err)
 	}
-	if err = d.Set("image_size_in_bytes", *image.ImageSizeInBytes); err != nil {
+	if err = d.Set("image_size_in_bytes", aws.Int64Value(image.ImageSizeInBytes)); err != nil {
 		return fmt.Errorf("failed to set image_size_in_bytes: %s", err)
 	}
+	if err := d.Set("image_tags", aws.StringValueSlice(image.ImageTags)); err != nil {
+		return fmt.Errorf("failed to set image_tags: %s", err)
+	}
 
 	tags := []string{}
 	for _, t := range image.ImageTags {