Use VAR=VAL syntax for environment variables

[piercebb]

Context

• Fixes .env file variable syntax is not compatible with latest docker-compose version 1.25.5 #624
• These changes unblock a common docker-compile error.
• Changes now use Docker's recommended syntax for Declaring default environment variables in .env files.

Summary of Changes

• Use VAR=VAL syntax for default environment variables
• Remove export VAR= syntax

Checklist

• Tested Mobile Responsiveness
• Added Unit Tests
• CI Passes
• Deploys to Heroku on test Correctly (Maintainers will handle)
• Added Documentation (Service and Code when required)

[DeeDeeG]

Paging @tkwidmer and @mi-wood, I think one of you (or both of you!) would know about this.

Do we need any of the environment variables in .env in this repo outside of Docker? Like in production/Heroku?

If you get the time to look at this, thanks in advance.

Edit: If so, how can we confirm they work without using export, but just plain setting them with var=value syntax?

[DeeDeeG]

This change was eventually made in #675.

Thank you for pointing out this fix.

(I will close this as it is redundant to the change from #675.)