[Organize Code] Add migrations in JH repo

When we want to add new migration file for JH specific feature:

% bundle exec rails g migration add_zentao_tracker_data
      invoke  active_record
      create    db/migrate/20210714025922_add_zentao_tracker_data.rb

Plan A

Follow the conventions of Rails, add new migration files db/migrate/ .

Due to the timestamp, we will not encounter conflicts from upstream.

advantage

• Conforms to convention, easy to understand
• Works for both migrations and initializers

disadvantage

• Add files outside the jh directory in JH Repo

Plan B

!58 (merged)

advantage

• All updates are in the jh directory

disadvantage

• Migration files are ok, we still need to find a solution for JH initializer files