@Override
    public Iterator<String> getKeys() {
        return System.getenv().keySet().iterator();
    }
Look up value from environment, but also look up common env var 'synonyms', with upper case and underscores instead of kebab/dot.
<p>
For example, <code>apiman.manager.api = APIMAN_MANAGER_API</code> or <code>apiman-manager-ui.api = APIMAN_MANAGER_UI_API</code>.

@author Marc Savy {@literal <marc@blackparrotlabs.io>}
common/config/src/main/java/io/apiman/common/config/EnvConfigurationWithSynonyms.java