[New Feature]: Add task-definition-arn input to deploy an existing revision

[hfalk]

Feature Description

Add a task-definition-arn input as an alternative to task-definition, for
deploying a task definition revision that is already registered in ECS. When it
is set, the action skips RegisterTaskDefinition and deploys the given revision
as-is.

    - name: Deploy an existing task definition revision
      uses: aws-actions/amazon-ecs-deploy-task-definition@v2
      with:
        task-definition-arn: arn:aws:ecs:us-east-2:123456789012:task-definition/my-task-definition-family:7
        service: my-service
        cluster: my-cluster
        wait-for-service-stability: true