Use terraform to config GCP proxy setup

With terraform (https://terraform.io) we can convert most of the infrastructure setup into code. This simplifies setting up a new proxy as well as providing reproducibility in the setup, eliminating human errors as much as possible.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=190634711

java/google/registry/proxy/kubernetes/proxy-deployment-alpha.yaml

@@ -14,10 +14,6 @@ spec:
       labels:
         app: proxy
     spec:
-      volumes:
-      - name: service-account-key
-        secret:
-          secretName: service-account
       containers:
       - name: proxy
         image: gcr.io/GCP_PROJECT/IMAGE_NAME:bazel
@@ -38,14 +34,9 @@ spec:
             port: health-check
           initialDelaySeconds: 15
           periodSeconds: 20
-        volumeMounts:
-        - name: service-account-key
-          mountPath: /var/secrets/google
         imagePullPolicy: Always
         args: ["--env", "alpha", "--log"]
         env:
-        - name: GOOGLE_APPLICATION_CREDENTIALS
-          value: /var/secrets/google/service-account-key.json
         - name: POD_ID
           valueFrom:
             fieldRef: