Feature request: Allow SAM to push container images to repository specified in template

### Describe your idea/feature/enhancement

I would like to be able to create a `Elastic Container Repository` in my SAM `template.yaml` and be able to use it to push `Container Images` using the `Metadata` for `AWS::Serverless::Function`

### Proposal

```yaml
StartMachineRepository:
Type: AWS::ECR::Repository
Properties:
RepositoryName: discord/start_function
StartMachineLambda:
Type: AWS::Serverless::Function
Properties:
PackageType: Image
Architectures:
- arm64
Metadata:
Dockerfile: functions/start_machine/Dockerfile.lambda
DockerContext: .
DockerTag: latest
DockerRepository: !Sub "${StartMachineRepository.RepositoryUri}"
```

### Additional Details

Start with the template.yaml example, the AWS::ECR::Repository resource, and the AWS::Serverless::Function image Metadata fields, including Dockerfile, DockerContext, DockerTag, and DockerRepository. Trace how SAM CLI handles image builds and pushes, then verify that a repository URI supplied from the template can receive the resulting container image.

Written by the indexing model from the issue text.