Configure CI/CD pipeline

Configure CI/CD pipeline for BE repo triggered on main branch, including 2 jobs:

• Job1: Build images (playground-be & upload) and push to the repositories with 2 tags (short git hash of commit, latest).
• Job2: Run the job on the Dev VM, download the .env files as the secure files configured on the pipeline and deploy the BE services by running ./start.sh script with the short git hash as image tag.

For reference: demo-backend-core