Standardize Build Event Protocol

Today, among different matured build tool solutions there exists several build event protocols that enable build telemetry use cases:

- [Bazel's BEP](https://bazel.build/remote/bep)
- [Buck2's BuckEvent](https://github.com/facebook/buck2/blob/ca3ccae0a8c6541c41be8248c99d4c80978ed039/app/buck2_data/data.proto#L21)
- [Chromium Siso's ResultStore](https://github.com/googleapis/googleapis/blob/master/google/devtools/resultstore/v2/resultstore_upload.proto)
- [Reclient's Event](https://github.com/bazelbuild/reclient/blob/ed0afeddb1b5f0d001a6c8578f000217f06534dc/internal/pkg/event/event.go#L19)

On top of these, many build tools and CI systems in the wild have started adopting a more generic telemetry system (Open Telemetry, Prometheus) for their CI/CD telemetry needs:

- https://github.com/mvisonneau/gitlab-ci-pipelines-exporter
- https://github.com/craigatk/opentelemetry-gradle-plugin
- https://github.com/inception-health/otel-export-trace-action
- https://github.com/zoidyzoidzoid/gitlab-honeycomb-buildevents-webhooks-sink
- https://github.com/craigatk/opentelemetry-gradle-plugin

So I want to start a discussion about a standardized Build Event Protocol so that different client and server implementations can agree on a common specification moving forward, and reduce overall fragmentation.

Please comment below if you are interested in adopting such a spec.

Start by comparing the linked Bazel BEP, Buck2 BuckEvent, Chromium ResultStore, and Reclient Event references, then review the listed OpenTelemetry and Prometheus examples. The issue is currently a discussion about agreement on a common specification; done would require a decided protocol scope and specification, not a single localized code change.

Written by the indexing model from the issue text.