Enable detection of gha-buildevents created spans

[DavidS]

This adds a meta.source top-level field to all events so that users can
easily distinguish between this and other sourced events.

[kvrhdn]

LGTM!

[kvrhdn]

Okay, the CI has run and I see now the meta.source field is only added to the parent trace and the last span (the gha-buildevents_post). Since we only create buildevents.txt in the post section, up until then buildevents won't know about meta.source...

I'm not sure what the best solution is here:

• we can create buildevents.txt at the beginning of the build, but then other programs should append their fields to this file (so gha-buildevents determines the location, the rest should follow)
• we keep it as is, though it feels inconsistent...

I'm more in favor of the first option, would this work with your workflows @DavidS ?

[kvrhdn]

I'll make a new release (and update the v1 tag) when we address this ☝🏻

[DavidS]

I definitely approve of the idea of getting gha-buildevents to manage the BUILDEVENT_FILE earlier. With the changes in #18 this is not an issue for our workflows, as we're setting BUILDEVENT_FILE and pre-filling fields there.