Added new migrations

• Added:
- new migrations

db/migrate/20200806162649_add_index_to_statuses_reply.rb

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+class AddIndexToStatusesReply < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+
+  def change
+    add_index :statuses, :reply, algorithm: :concurrently
+  end
+end

db/migrate/20200806174026_create_group_join_requests.rb

@@ -0,0 +1,14 @@
+class CreateGroupJoinRequests < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+
+  def change
+    create_table :group_join_requests do |t|
+      t.belongs_to :account, foreign_key: { on_delete: :cascade }, null: false
+      t.belongs_to :group, foreign_key: { on_delete: :cascade }, null: false
+
+      t.timestamps null: false
+    end
+
+    add_index :group_join_requests, [:account_id, :group_id], unique: true, algorithm: :concurrently
+  end
+end

db/migrate/20200806231714_add_indexes_to_status_stats.rb

@@ -0,0 +1,10 @@
+class AddIndexesToStatusStats < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+
+  def change
+    add_index :status_stats, :updated_at, algorithm: :concurrently
+    add_index :status_stats, :replies_count, algorithm: :concurrently
+    add_index :status_stats, :reblogs_count, algorithm: :concurrently
+    add_index :status_stats, :favourites_count, algorithm: :concurrently
+  end
+end