Chore: Enable Users to create multiple accounts (#440)

Addresses: #402
- migrations to split roles and other attributes from users table
- make changes in code to accommodate this change

Co-authored-by: Sojan Jose <sojan@pepalo.com>
Co-authored-by: Pranav Raj Sreepuram <pranavrajs@gmail.com>

db/seeds.rb

@@ -1,9 +1,15 @@
 account = Account.create!(name: 'Acme Inc')
 
-user = User.new(name: 'John', email: 'john@acme.inc', password: '123456', account: account, role: :administrator)
+user = User.new(name: 'John', email: 'john@acme.inc', password: '123456')
 user.skip_confirmation!
 user.save!
 
+AccountUser.create!(
+  account_id: account.id,
+  user_id: user.id,
+  role: :administrator
+)
+
 web_widget = Channel::WebWidget.create!(account: account, website_name: 'Acme', website_url: 'https://acme.inc')
 
 inbox = Inbox.create!(channel: web_widget, account: account, name: 'Acme Support')