[Dashboard De-Angular] Add and render dashboard editor page

[abbyhu2000]

Render the main dashboard editing page using react component.

<dashboard-app
  class="app-container dshAppContainer"
  ng-class="{'dshAppContainer--withMargins': model.useMargins}"
>
  <div id="dashboardChrome"></div>
  <h1 class="euiScreenReaderOnly">{{screenTitle}}</h1>
  <div id="dashboardViewport"></div>

</dashboard-app>

• Empty page
  • [Dashboard De-Angular] Render empty dashboard screen when creating new dashboards #4346
• Be able to add existing or create new visualization embeddable
  • [Dashboard De-Angular] Add new/existing visualizations to dashboard #4257
• Full screen/exit full screen
• Embedded mode/exist embedded mode
• Darkmode
• All panel actions working correctly: expanded panel
  • [Dashboard De-Angular] Add and render dashboard editor page #4003
• UI bootstrap
• investigate if resetState() is needed here when saving the dashboard
• permission controls