Usage for master branch

[paulirish]

as you can tell i'm adopting bundletracker for Lighthouse. :)

we were using bundlesize but it's terrible and i hate it.

the first priority is to get the historical trendlines of our build sizes. I managed to iterate through 18 months of git history and upload all those builds:
https://lh-build-tracker.herokuapp.com/builds/limit/1000

then, i wanted to get some CI set up to upload build stats for all our new commits on master. so I wrote a ghaction workflow to do that: paulirish/lighthouse#57

However, the build-tracker-action basically expects to only run on: pull_request, it appears.

(from https://github.com/paulirish/lighthouse/runs/520463822)

It's erroring on context.payload.pull_request.

For whatever reason I didn't think a workflow that's on: pull_request would run on push to master, but... does it?

[paularmstrong]

In all honesty, I copied most of how this was done from https://github.com/preactjs/compressed-size-action. There's definitely no handling for anything outside of PRs.

For push, I'm currently using yarn bt-cli upload-build directly, but it would be really nice to make this action able to work for any stage that an action can run at.