[BUG] Unable to set env var default values within template config.

[flancast90]

Describe the bug
Default env variable values cannot be set in config.json files for templates.

Expected behavior
The optimal environment variable creation process would allow a template creator to set a default value within the config file, which could then be edited as-needed by users. This would streamline actions such as using dynamic base URLs for APIs, as shown in @paulkr's comment in #41.

Example

"envVars": {
    "FAKE_API_KEY": "123456"
  },

[paulkr]

Since each environment variable has a value for the development (test) and production (live) environments, you have to specify both values in the configuration.

Example:

{
  "envVars": {
    "FAKE_API_KEY": {
      "development": "fake-development-api-key",
      "production": "fake-production-api-key"
    }
  }
}