Misk should support some concept of environments

[JGulbronson]

This will be useful when determining which yaml files for parse for config, as mentioned in #1. Examples of environments are testing, staging, production, etc.

A simple implementation could just be a String that gets bound so you can inject it like

@Inject @Env String environment

Misk can provide a module that binds based of an environment variable. Alternatively a module can statically provide an environment, and then an app can select which to install.

[maniksurtani]

Should they be Strings, though? Maybe an Environment interface, and the default impl could be an enum with the more common set of {DEVELOPMENT, STAGING, PRODUCTION}.