Adds CSV loader for SearchEvents

https://mitlibraries.atlassian.net/browse/TCO-35

This loader is not meant to be used in production, but instead be a
convenience for loading data into development environments to allow for
easier development of detection algorithms or reporting.

There is a Dataclip that exports data in the expected format, but it
is also easy to generate your own file as it is just `term` and
`timestamp` that is expected.

Currently, `source` is provided via CLI but if we find it would be
better to include the source in the CSV that would be an easy change
to make.

lib/tasks/loader.rake

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+require 'csv'
+
+# Loaders can bulk load data
+namespace :loader do
+  # csv loader can bulk load SearchEvents and Terms
+  #
+  # @note the csv should be formated as `term phrase`, `timestamp`. A dataclip is available that can export in this
+  #   format.
+  # @example
+  # bin/rails loader:csv['local_path_to_file.csv', 'some-source-to-use-for-all-loaded-records']
+  #
+  # @param path [String] local file path to a CSV file to load
+  # @param source [String] source name to load the data under
+  desc 'Load search_events from csv'
+  task :csv, %i[path source] => :environment do |_task, args|
+    raise ArgumentError.new('Path is required') unless args.path.present?
+    raise ArgumentError.new('Source is required') unless args.source.present?
+
+    Rails.logger.info("Loading data from #{args.path}")
+
+    CSV.foreach(args.path) do |row|
+      term = Term.create_or_find_by!(phrase: row.first)
+      term.search_events.create!(source: args.source, created_at: row.last)
+    end
+  end
+end