chore(build): Update cloudbuild.yaml file (spinnaker#3063)

The currently checked-in Google Cloud Build configs have not
been maintained and are no longer used when producing the official
Spinnaker releases. Instead, the build process generates a GCB
config on-the-fly and uses that.

To make the process more clear and make it easier for others to
reproduce the builds, commit the GCB config that is auto-generated
to the repo. Also, delete the unused cloudbuild-tagged.yaml.

cloudbuild.yaml

@@ -1,10 +1,13 @@
 steps:
-- name: 'spinnakerrelease/gradle_cache'
+- name: gcr.io/spinnaker-marketplace/gradle_cache
   env: ["GRADLE_USER_HOME=/gradle_cache/.gradle"]
   entrypoint: "bash"
-  args: [ "-c", "./gradlew orca-web:installDist -x test"]
-- name: 'gcr.io/cloud-builders/docker'
-  args: ["build", "-t", "gcr.io/$PROJECT_ID/$REPO_NAME:$COMMIT_SHA", "-t", "gcr.io/$PROJECT_ID/$REPO_NAME:latest", "-f", "Dockerfile.slim", "."]
+  args: ["-c", "./gradlew orca-web:installDist -x test"]
+- name: gcr.io/cloud-builders/docker
+  args: ["build", "-t", "gcr.io/$PROJECT_ID/$REPO_NAME:$TAG_NAME", "-f", "Dockerfile.slim", "."]
+  env: ["GRADLE_USER_HOME=/gradle_cache/.gradle"]
 images:
-- 'gcr.io/$PROJECT_ID/$REPO_NAME:$COMMIT_SHA'
-- 'gcr.io/$PROJECT_ID/$REPO_NAME:latest'
+- gcr.io/$PROJECT_ID/$REPO_NAME:$TAG_NAME
+timeout: 3600s
+options:
+  machineType: N1_HIGHCPU_8