Export public database dumps to BigQuery.

* Export daily public database dumps to BigQuery and Google Cloud Storage.
* Only data visible to anonymous users is exported. Some tables have
  null or missing fields because of this.
* The bans table is excluded because some bans have an expires_at
  timestamp set beyond year 9999, which BigQuery doesn't support.
* The favorites table is excluded because it's too slow to dump (it
  doesn't have an id index, which is needed by find_each).
* Version tables are excluded because dumping them every day is
  inefficient, streaming insertions should be used instead.

Links:

* https://console.cloud.google.com/bigquery?project=danbooru1
* https://console.cloud.google.com/storage/browser/danbooru_public
* https://storage.googleapis.com/danbooru_public/data/posts.json

app/jobs/bigquery_export_job.rb

@@ -0,0 +1,7 @@
+class BigqueryExportJob < ApplicationJob
+  retry_on Exception, attempts: 0
+
+  def perform(model:, **options)
+    BigqueryExportService.new(model, **options).export!
+  end
+end