Add migrations for version control snippets

Add columns `repository_storage` and `storage_version`
to snippets.

changelogs/unreleased/fj-add-migrations-snippet-repository.yml

+---
+title: Add migrations for version control snippets
+merge_request: 22275
+author:
+type: added

db/migrate/20191218124915_add_repository_storage_to_snippets.rb

+# frozen_string_literal: true
+
+class AddRepositoryStorageToSnippets < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_column_with_default( # rubocop:disable Migration/AddColumnWithDefault
+      :snippets,
+      :repository_storage,
+      :string,
+      default: 'default',
+      limit: 255,
+      allow_null: false
+    )
+  end
+
+  def down
+    remove_column(:snippets, :repository_storage)
+  end
+end

db/migrate/20191218125015_add_storage_version_to_snippets.rb

+# frozen_string_literal: true
+
+class AddStorageVersionToSnippets < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+  disable_ddl_transaction!
+
+  def up
+    add_column_with_default( # rubocop:disable Migration/AddColumnWithDefault
+      :snippets,
+      :storage_version,
+      :integer,
+      default: 2,
+      allow_null: false
+    )
+  end
+
+  def down
+    remove_column(:snippets, :storage_version)
+  end
+end

db/schema.rb

@@ -3803,6 +3803,8 @@ ActiveRecord::Schema.define(version: 2020_01_06_071113) do
     t.string "encrypted_secret_token", limit: 255
     t.string "encrypted_secret_token_iv", limit: 255
     t.boolean "secret", default: false, null: false
+    t.string "repository_storage", limit: 255, default: "default", null: false
+    t.integer "storage_version", default: 2, null: false
     t.index ["author_id"], name: "index_snippets_on_author_id"
     t.index ["content"], name: "index_snippets_on_content_trigram", opclass: :gin_trgm_ops, using: :gin
     t.index ["created_at"], name: "index_snippets_on_created_at"

lib/gitlab/import_export/import_export.yml

@@ -172,6 +172,8 @@ excluded_attributes:
     - :secret
     - :encrypted_secret_token
     - :encrypted_secret_token_iv
+    - :repository_storage
+    - :storage_version
   merge_request_diff:
     - :external_diff
     - :stored_externally