Allow EnvironmentParameterStore to cast environment values to non-string types

[cspray]

The getenv function used by EnvironmentParameterStore will result in a string always being returned the way the class is currently implemented. The return type on this method is currently erroneous; it is declared as string|array|false but will never return array nor false.

Ideally this parameter store would be aware of the type of the parameter it is being injected into and cast where appropriate. This could allow declaring configuration provided through the environment with proper types (e.g. a database configuration specifying a port as an integer).