Add Redis HLL metric generator

lib/generators/gitlab/usage_metric_definition/redis_hll_generator.rb

+# frozen_string_literal: true
+
+require 'rails/generators'
+
+module Gitlab
+  module UsageMetricDefinition
+    class RedisHllGenerator < Rails::Generators::Base
+      desc 'Generates a metric definition .yml file with defaults for Redis HLL.'
+
+      argument :category, type: :string, desc: "Category name"
+      argument :event, type: :string, desc: "Event name"
+
+      def create_metrics
+        generate 'gitlab:usage_metric_definition', "#{key_path}_weekly --dir 7d"
+        generate 'gitlab:usage_metric_definition', "#{key_path}_monthly --dir 28d"
+      end
+
+      private
+
+      def key_path
+        "redis_hll_counters.#{category}.#{event}"
+      end
+    end
+  end
+end