Open-Sourcing TestGrid Frontend

Currently, the backend of TestGrid is open-sourced, however, the frontend is not yet open-sourced.

Open-Sourcing of Testgrid Frontend would help in provisioning a standalone TestGrid cluster without the reference of testgrid.k8s.io. This may also help in resolving issues like https://github.com/GoogleCloudPlatform/testgrid/issues/489#issuecomment-853416225 where the web app cannot render S3 data. Testgrid has a hard requirement that Prow JobLogs should be stored only in GCS bucket.

Currently, the TestGrid Frontend can be used as a service to render it on testgrid.k8s.io/r/bucket-name. However, this requires explicit read access to be provided for the service account `k8s-testgrid@appspot.gserviceaccount.com` to the testgrid bucket config.

Previously, there have been discussions on this topic, linking them here for context https://github.com/kubernetes/test-infra/issues/10409.

What needs to be done for open-sourcing of TestGrid Frontend? Is there any help required?