ConfigMap Reducer

[moogar0880]

The purpose of this issue is to implement a reducer for the ConfigStore.

This reducer will be responsible for generating a single ConfigMap comprised of the resolvable fields stored in ConfigStore, resulting in the effective configuration for the wrapping application. For example a configuration like

{
    "DefaultLevel": {
        "foo": "bar",
        "jenny": 8675309
    },
    "OverrideLevel": {
        "foo": "baz"
    }
}

should produce a reduced ConfigMap that looks like this:

{
    "foo": "baz",
    "jenny": 8675309
}

This could prove useful for services that maintain a relatively large configuration sourced from multiple locations that may wish to examine the effective state of their configuration.