DEV: move discourse_dev gem to the core. (#13360)

And get avatar images from `discourse_dev_assets` gem.

lib/discourse_dev/group.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+require 'discourse_dev/record'
+require 'rails'
+require 'faker'
+
+module DiscourseDev
+  class Group < Record
+
+    def initialize
+      super(::Group, DiscourseDev.config.group[:count])
+    end
+
+    def data
+      {
+        name: Faker::Discourse.unique.group,
+        public_exit: Faker::Boolean.boolean,
+        public_admission: Faker::Boolean.boolean,
+        primary_group: Faker::Boolean.boolean,
+        created_at: Faker::Time.between(from: DiscourseDev.config.start_date, to: DateTime.now),
+      }
+    end
+
+    def create!
+      super do |group|
+        if Faker::Boolean.boolean
+          group.add_owner(::Discourse.system_user)
+          group.allow_membership_requests = true
+          group.save!
+        end
+      end
+    end
+
+    def self.random
+      super(::Group)
+    end
+  end
+end