[APM] Errors overview list redesign

[formgeist]

Summary

Related to elastic/apm#264 which provides a larger revamp of the Errors experience in APM, we're proposing some new features and improvements to the Errors list table.

Solution

The new errors list table simplifies the errors information displayed while allowing for some new context to be provided for each error group.

• Remove the error group ID
• Remove the error type
• Decrease the font size of the error message link
• Add transaction name link which will link to a sample transaction, providing a shortcut to view the trace timeline for a sample in which this error occurred.
• Add new "First seen" relative timestamp. The first seen will be the timestamp of the first error occurrence for the error group. This needs to be kept in record for rollup data as well to be able to show a "new error" indicator.
• Show "new error" indicator if the first seen occurrence is within the last 7 days.
• Change "Last occurrence" to "Last seen" label

Open questions

• The first seen occurrence, we'll need to figure out how we want to save a record of the first occurrence of a given error group.

[elasticmachine]

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

[formgeist]

@alex-fedotyev Do you agree that we can close this design overhaul for now because we need to re-evaluate the Errors experience at some point and it doesn't make sense to have this design waiting for implementation at this time?

[graphaelli]

That makes sense, closing this out.