Add step to apply latest tag to docker image for releases

[kmcginnes]

Description

Adds a step to the Docker workflow that will only be run when performing a release. This step will assign the latest tag to the build and push to the ECR repository.

Validation

I tested this by running the workflow locally using act. I created a public ECR repo in my AWS account and used my own secrets to perform the push.

I verified the new step will not run when image_tag != 'release'. I also verified that when it does run for a release it will push both the version tag and the latest tag. It will also push the SageMaker build with the sagemaker-latest tag. It will replace any existing latest tags with the new version.

Related Issues

Addresses #315

Check List

• I confirm that my contribution is made under the terms of the Apache 2.0 license.
• I have run pnpm run checks to ensure code compiles and meets standards.
• I have run pnpm run test to check if all tests are passing.
• I've covered new added functionality with unit tests if necessary.