Configure .env for environment variables

[jmiranda]

Details
https://docs.expo.io/guides/environment-variables/

Expected Behaviors

• Should be used for any environment (development, staging, production) to store environment variables that will be used for API URLs, keys, secrets, etc.
• Should not store .env file in repository (need to figure out way to copy variables to compiled application without leaking secrets)

[Bluesir9]

react-native-dotenv is the standard way to manage environment variables in react-native apps. However it doesn't seem to be playing well with Expo.

So for now an Environment.ts configuration object has been added to the project. Environment.ts just defines the shape of the environment configuration and the developer running the project is expected to provide the actual configuration in a file called EnvironmentActual.ts file that exports the actual object. Since this configuration can change from developer to developer, the file has been excluded from the repo.

While for now this will be good enough, we should consider revisiting how react-native-dotenv can be made to work sometime in the future.