[Feature Request] Show event label on the build detail page.

[kumada626]

What happened: We want to know event label in the build detail page. Event Labels: https://docs.screwdriver.cd/user-guide/metadata#event-labels

What you expected to happen: If the event has label, we'd like to what the event label is in the build detail page.

How to reproduce it:

1. Add label to the event.
2. Visit the build detail page, we don't know what the event label is.