fail app startup on missing env config

[jgunnCO]

Description

Building or starting the app will now fail if config defined in the .env.example files is missing from the environment.

Type of change

Please check the relevant options.

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).
• This change requires a documentation update.

How Has This Been Tested?

Please describe the tests that you ran to verify your changes:

• Unit Test

• Integration Test (if applicable)

• End to End Test (if applicable)

Screenshots (if appropriate):

Please attach screenshots of the change if it is a UI change:

Checklist:

• If I have listed dependencies above, I have ensured that they are present in the target branch.
• I have performed a self-review of my code.
• I have commented my code in hard-to-understand areas.
• I have made corresponding changes to the documentation where applicable.
• I have ran cypress tests and they all pass locally.