CI Template for Salesforce/Apex

With the growth of the new Salesforce DX platform, Salesforce developers are looking for a CI/CD solution. It would be great if there were a CI/CD template for Apex/DX projects. Ideally, we'd have this available before the Salesforce developer conference TrailheaDX on May 29, 2019.

@mayanktahil and I are working on this.

Related to #59664 (moved)