This image builds https://github.com/grafana/flagger-k6-webhook with custom overrides.
gcloud builds submit --project kraken-v2-dev --config ./cloudbuild_flagger_k6.yml --substitutions='_PROJECT=kraken-v2-dev'
gcloud builds submit --project kraken-v2-prod --config ./cloudbuild_flagger_k6.yml --substitutions='_PROJECT=kraken-v2-prod'