Allowed .env file in source control for test-utils setup

refs https://github.com/TryGhost/members.js/issues/5

- We want to allow .env in source control mainly to use react-testing-library's recommended setup for common test-utils. It uses .env file to define NODE_PATH, which helps in avoiding relative imports in tests as we keep test files next to UI components.
- CRA also by default suggests committing .env files to source control

ghost/portal/.gitignore

@@ -57,7 +57,7 @@ typings/
 .yarn-integrity
 
 # dotenv environment variables file
-.env
+.env.*
 
 # IDE
 .idea/*
@@ -72,8 +72,9 @@ typings/
 umd/
 build/
 
-## config
-.env.local
-.env.development.local
-.env.test.local
-.env.production.local
+# Allow .env file
+!.env
+## We use .env file to define NODE_PATH as recommended test-utils setup pattern to avoid relative imports.
+# Refs: https://testing-library.com/docs/react-testing-library/setup#jest-and-create-react-app
+# CRA also suggests `.env` files should be checked into source control
+# Ref: https://create-react-app.dev/docs/adding-custom-environment-variables/#adding-development-environment-variables-in-env