CICD Include PR number from build in the terraform workspace name to avoid deployment collisions during PR branch CI/CD processes

[KeithJRome]

Description

As a developer, I'd like to have the CI/CD process perform any test deployments for my PR in a way that ensures no conflict with other PRs (or with master), in order to avoid any workspace or naming conflicts.

It was determined that a good way to achieve this would be to modify our YAML pipeline to incorporate the PR number (if triggered via PR) into the workspace name. The workspace name is currently assembled by combining the workspacePrefix in the top-level YAML with the build environment (ie "devint"/etc).

(additional scope 10/3/2019):
To reduce risk to other ongoing work, we decided to fold additional functionality into this story. This includes:

• Ability to disable/enable PR isolation of deployments from top-level YAML per environment/template
• Ability to disable/enable name randomization from top-level YAML per environment/template

Acceptance Criteria

Reference: [Done-Done Checklist] (https://github.com/Microsoft/code-with-engineering-playbook/blob/master/Engineering/BestPractices/DoneDone.md)

• CI/CD deployments from master branch should continue to operate the same as they do prior to this change (no change to workspace and resource naming)
• CI/CD deployments from Pull Request branches should insert the PR number into the workspace name (which then should cascade into the resource names)
• Use of PR number in workspace name should be configurable through pipeline YAML
• Use of random characters in resource names should be configurable through pipeline YAML

Resources

Tasks

Stories are intended to be completed in a single sprint; if task breakdown creates addition work then team should discuss promoting the Story to an Epic.
Reference: [Minimal Valuable Slices] (https://github.com/Microsoft/code-with-engineering-playbook/blob/master/Engineering/BestPractices/MinimalSlices.md)

Reference: [How to Write Better Tasks] (http://agilebutpragmatic.blogspot.com/2012/04/splitting-story-into-tasks-how-to-write.html)

Assignee should break down work into tasks here

[ThePhen]

It might be important that someone/something clean-up AZ resources, once a PR is merged/closed (or else the resources will keep billing).

[erikschlegel]

I love the idea of including the PR id within the workspace prefix.