Ensure image tag is immutable for Amazon Elastic Container Registry (Amazon ECR) Repository

Image tags are not immutable for AWS ECR Repository. This may allow overwriting tags.

In AWS Console -

1. Sign in to the AWS Console and open the ECR Console.
2. Select the repository you wish to update.
3. Click Edit.
4. Set Tag immutability to Enabled.
5. Select Save.

In Terraform -

1. In the aws_ecr_repository resource, set the image_tag_mutability field to IMMUTABLE.

References:
https://docs.aws.amazon.com/AmazonECR/latest/userguide/image-tag-mutability.html
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/ecr_repository