title: Use workbench.colorCustomizations in extension?
body: <ol>
  <li>Users can customize the UI using <code>workbench.colorCustomizations</code> settings.</li>
  <li>I'd like to <strong>ship such customization in my color theme</strong> <a href="https://marketplace.visualstudio.com/items?itemName=eppz.eppz-code" rel="noreferrer">eppz! (C# theme for Unity)</a>.</li>
  <li>How?</li>
  </ol>
  
  <hr>
  
  <p>I tried to contribute these values to my extension, but nor <code>configuration</code>, nor <code>configurationDefaults</code> contribution points worked. As these customizations are actually workbench user settings, I'm actually asking <strong>how to contribute value overrides to <code>settings.json</code> in an extension</strong>.</p>