Add usage_metric_definition generator to generate new yaml metric file

generator_templates/usage_metric_definition/metric_definition.yml

+# See Usage Ping metrics dictionary docs https://docs.gitlab.com/ee/development/usage_ping/metrics_dictionary.html
+key_path: <%= key_path %>
+value_type:
+product_category:
+stage:
+status:
+milestone:
+introduced_by_url:
+group:
+time_frame: <%= time_frame %>
+data_source:
+distribution: <%= distribution %>
+# tier: ['free', 'starter', 'premium', 'ultimate', 'bronze', 'silver', 'gold']
+tier:

lib/generators/gitlab/usage_metric_definition_generator.rb

+# frozen_string_literal: true
+
+require 'rails/generators'
+
+module Gitlab
+  class UsageMetricDefinitionGenerator < Rails::Generators::Base
+    Directory = Struct.new(:name, :time_frame) do
+      def match?(str)
+        (name == str || time_frame == str) && str != 'none'
+      end
+    end
+
+    TIME_FRAME_DIRS = [
+      Directory.new('counts_7d',  '7d'),
+      Directory.new('counts_28d', '28d'),
+      Directory.new('counts_all', 'all'),
+      Directory.new('settings',   'none'),
+      Directory.new('license',    'none')
+    ].freeze
+
+    VALID_INPUT_DIRS = (TIME_FRAME_DIRS.flat_map { |d| [d.name, d.time_frame] } - %w(none)).freeze
+
+    source_root File.expand_path('../../../generator_templates/usage_metric_definition', __dir__)
+
+    desc 'Generates a metric definition yml file'
+
+    class_option :ee, type: :boolean, optional: true, default: false, desc: 'Indicates if metric is for ee'
+    class_option :dir,
+      type: :string, desc: "Indicates the metric location. It must be one of: #{VALID_INPUT_DIRS.join(', ')}"
+
+    argument :key_path, type: :string, desc: 'Unique JSON key path for the metric'
+
+    def create_metric_file
+      validate!
+
+      template "metric_definition.yml", file_path
+    end
+
+    def time_frame
+      directory&.time_frame
+    end
+
+    def distribution
+      value = ['ce']
+      value << 'ee' if ee?
+      value
+    end
+
+    private
+
+    def file_path
+      path = File.join('config', 'metrics', directory&.name, "#{file_name}.yml")
+      path = File.join('ee', path) if ee?
+      path
+    end
+
+    def validate!
+      raise "--dir option is required" unless input_dir.present?
+      raise "Invalid dir #{input_dir}, allowed options are #{VALID_INPUT_DIRS.join(', ')}" unless directory.present?
+    end
+
+    def ee?
+      options[:ee]
+    end
+
+    def input_dir
+      options[:dir]
+    end
+
+    def file_name
+      key_path.split('.').last
+    end
+
+    def directory
+      @directory ||= TIME_FRAME_DIRS.find { |d| d.match?(input_dir) }
+    end
+  end
+end