Allow Admin users to see Admin API analytics on the Dashboard

[brylie]

Currently, there is no way for Admin users to view usage statistics about the Admin API. This may be useful for diagnostic purposes, such as detecting performance bottlenecks.

Add an option to the Select API dropdown, that only Admin users can see, so that we can display analytics from the /api-umbrella/ endpoint on the dashboard:

Example code

<!-- Admin API -->
<optgroup label="Admin" >
  <option value="/api-umbrella" >
    Admin API
  </option>
</optgroup>

[brylie]

Ping @frenchbread

[bajiat]

@frenchbread What is your estimate for this?

[frenchbread]

@bajiat Done, pushing the code..