Optimise GCP cloud spend

[upodroid]

CNCF asked us to optimise our GCP spend and reduce waste. I identified a few improvements:

1. GCS buckets in Boskos projects cost a lot. So I deleted them all and migrated GCR to AR.(The image registry address is the same but its backend is Artifact Registry with 7 day expiry policy)
2. Boskos projects are managed in Terraform fully
3. I optimised GKE autoscaling policies to be downscale more aggressively.

/cc @cardil @dprotaso

[dprotaso]

/lgtm
/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dprotaso, upodroid

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[knative-prow]

@upodroid: Updated the job-config configmap in namespace default at cluster default using the following files:

• key infra.yaml using file prow/jobs/custom/infra.yaml

In response to this:

CNCF asked us to optimise our GCP spend and reduce waste. I identified a few improvements:

1. GCS buckets in Boskos projects cost a lot. So I deleted them all and migrated GCR to AR.(The image registry address is the same but its backend is Artifact Registry with 7 day expiry policy)
2. Boskos projects are managed in Terraform fully
3. I optimised GKE autoscaling policies to be downscale more aggressively.

/cc @cardil @dprotaso

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