feature: (do not merge) add new branch to support jump-start-solution

[Shabirmean]

Description

• This change is not supposed to be merged in.
• The PR is open only as a visualizer to see what changes were made on the jss branch
• This branch is created to add Spanner as a backend to the the Point of sale application
• This modification is done to make this application ready for the "Dynamic webapp using Java on GKE" Jump Start Solution
• Artifacts from this branch are used by the Terraform script in: https://github.com/GoogleCloudPlatform/terraform-example-java-dynamic-point-of-sale