[ECR Public] [request]: ScanOnPush and immutability for public containers

### Community Note

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**Tell us about your request**
Similar to

```
aws ecr create-repository \
--repository-name ${DOCKER_REPOSITORY} \
--image-tag-mutability IMMUTABLE \
--image-scanning-configuration scanOnPush=true
```
References:

1. https://docs.aws.amazon.com/AmazonECR/latest/userguide/image-tag-mutability.html
1. https://docs.aws.amazon.com/AmazonECR/latest/userguide/image-scanning.html

Support `--image-tag-mutability` and `--image-scanning-configuration scanOnPush=true` for `aws ecr-public`.
Example:

```
aws ecr-public create-repository \
--repository-name ${DOCKER_REPOSITORY} \
--image-tag-mutability IMMUTABLE \
--image-scanning-configuration scanOnPush=true
````

**Which service(s) is this request for?**
ECR

Start with the aws ecr-public create-repository command and the linked AWS documentation for image tag mutability and image scanning. Determine where this roadmap request would be implemented and verify that both options are supported for public repositories; done means the example command works with --image-tag-mutability and --image-scanning-configuration scanOnPush=true.

Written by the indexing model from the issue text.