Small improvements for Cycle Analytics

• Restores legend text for events column
• Ensures event objects definition

/cc @jameslopez

merged

@alfredo1 I'm not sure this made it to 8.17? If not, we may have to add the Pick into Stable label for this to be picked

added ~149423 label

@jameslopez ah sorry, I just added the label

Removing Pick into Stable as this seems to be the same as https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9153 - @alfredo1 feel free to ping me if not!

removed ~149423 label