refactor: move current seeds.rb script to new DevStarter module (lib/seed/seeder.rb)

[kolharsam]

Ref ticket: #762

This pull request refactors the database seeding process by moving the logic into a new module and class, and organizing constants into a separate file.

• db/seeds.rb: It now just directly calls Seed::DevStarter.call.
• lib/seed/dev_starter.rb: Created a new Seed::DevStarter class that encapsulates the seeding logic for admin, owner, and developer users (as it was present in the earlier seeds.rb file)
• lib/seed/constants.rb: Moved constants for admin, owner, and developer user details into a separate file

This starts a new series of PRs that are meant to eventually help resolve #762

[kitallis]

Approving, left a small comment.

[kitallis]

issue this needn't be called like this, we can just call it like self.class.create_admin_user and remove the private. But better yet, since this class doesn't have state yet, the point of the class is sort of very low value. Classes encapsulate state. But it may in the future, so I would recommend just do something like:

def self.call
  new.call
end

def call
  create_admin_user
  ..
end

And make all those class methods, instance methods (and you can keep them private).