As an AdminCentral user, I want a simple message clearly indicating that some content is not available, so that I know what is happening in the system and know what to do.

Currently if a REST endpoint is not available (Thanks to MGNLRESTCL-76)  the content is not displayed and an error is written to the log, but the user does not know what happened or why.

UI elements that can have a REST Datasource should be able to gracefully handle the endpoint being unavailable. Probably showing a clear message where the content would normally be displayed - in the App, in the Chooser, in the Select field, etc. Something like "Content not available. Please try again later. If this problem persists contact your system administrator."

Acceptance criteria

• Handle browser subapp (obstrusive)
• Handle select box (non-obstrusive)
• Handle link field (non-obstrusive)
• REST supplier? —not an issue
• (Did I miss a key UI element?)

Highlight dependency on UI improvement for fields if needed.