Publish images for sample applications used in the App Mesh examples walkthroughs

**Description**
Currently, every time a user wants to try any of the walkthrough examples in this repo, they need to build the sample application images, publish them to ECR and then use them in their App Mesh setup. This also requires the users to have Docker installed on their machine to build the images.

**Proposed change**
We should publish images for sample applications used in the App Mesh walkthroughs and by default use the published images. If a user wants to modify the application code or override, they should have the ability to do so.