Repo should have automatic CI for 3rd-party contributors

[artem-zinnatullin]

Buildkite is a CI company, Buildkite CI is quite awesome. This repo as any other open source repo maintained by Buildkite should strive to provide best CI experience for both maintainers and 3rd-party contributors (most of who are paid Buildkite users).

As of right now, this repo CI requires manual approval by Buildkite employees to run on 3rd-party PRs. This is a significant bottleneck for external contributors as it prevents us from iterating on PRs at our own pace while ensuring full compliance with repo CI checks.

I think it's reasonable to expect great CI experience on a repo maintained by CI company 😬