[APM] Missing error in waterfall

[sorenlouv]

Problem
Sometimes the ui will indicate that a trace contains an error in the summary information (above waterfall) without indicating on the waterfall where the error occurred. This means there is no way to navigate to the error or figure out anything about the error.

Cause
This behaviour occurs if the user happens to navigate to a downstream section of a trace and the error occurred upstream.

Workaround
The user can click "View full trace" which will reveal the transaction containing the error (/dashboard)

[elasticmachine]

Pinging @elastic/apm-ui (Team:apm)

[formgeist]

Discussed this with @sqren in a call earlier and we came to the following conclusions;

We have an open redesign for the Trace timeline to no longer include it within the Transaction detail of a selected service, but instead display the Trace on its own in a separate view. This means no longer only visualizing the selected transaction, but the full trace always. We don't have to wait until the redesign to always show the full trace.

Another (really simple) option is to remove the error count from the trace detail header because the information is confusing when viewing a single transaction that does not have errors.

[formgeist]

I've removed the needs design label and unassigned myself, as I have proposed a solution above that will make the error count badge not necessary. We can move this to the backlog, I don't have a particular indication of priority.