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

Gemfile

@@ -47,6 +47,8 @@ gem 'nokogiri'
 gem 'view_component', require: 'view_component/engine'
 gem 'tzinfo-data'
 gem 'hsluv'
+gem 'google-cloud-bigquery', require: "google/cloud/bigquery"
+gem 'google-cloud-storage', require: "google/cloud/storage"
 
 group :production, :staging do
   gem 'unicorn', :platforms => :ruby