Send the exception message to the client instead of only the Client Error Code

Now when something fails due to a client error, we are completely in the dark: The HST logs at info level, so not visible in logs. The exception message is not send to the browser, only the ClientError code

Instead, the ClientError code should be in a different field and the message should contain the exception message.

In the channel mngr UI we should show the exception message when clicking for example [?] to see what the exception was: Otherwise, we can never help customers when something goes wrong.