Add caution message around "internal" API

[drew-russell]

Describe the solution you'd like

For API calls that fall under the "internal" API version we include the following in the Response Header:

warning: 199 - This API Resource is subject to ongoing development. 
The endpoint and the parameters may change in the future. Only use this 
API when necessary. USE AT YOUR OWN RISK.

To prevent any potential issues with the API version we need to include a similar message in the Chrome extension. We could:

• Add a UI element that "highlights" the internal API calls and then provides additional context (similar to the message above). Or maybe just add a UI element (think a small info icon) for all internal endpoints
• Make sure to call out the warning in the API documentation (Link to API Documentation #14)