Master build validation on merge for core environment templates

[charleszipp]

Description

As an engineer, I would like to be able to validate my core environment templates, so that I prevent faulty template changes from being deployed

Acceptance Criteria

Scenario: Changes merged to master have valid syntax
given code changes to the core environment templates have valid syntax
when a pull request is opened for these changes
then a build should be triggered
and the build should pass

Scenario: Changes merged to master have invalid syntax

given code changes to the core environment templates have invalid syntax
when a pull request is opened for these changes
then a build should be triggered
and the build should fail
and the build log should indicate the validation errors that exist in the templates
and the pull request merge should be blocked

Notes:

• Clarify "syntax" language.
• Make sure we're clear that this is a master branch validation.