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>

app/models/account_user.rb

@@ -0,0 +1,48 @@
+# == Schema Information
+#
+# Table name: account_users
+#
+#  id         :bigint           not null, primary key
+#  role       :integer          default("agent")
+#  created_at :datetime         not null
+#  updated_at :datetime         not null
+#  account_id :bigint
+#  inviter_id :bigint
+#  user_id    :bigint
+#
+# Indexes
+#
+#  index_account_users_on_account_id  (account_id)
+#  index_account_users_on_user_id     (user_id)
+#  uniq_user_id_per_account_id        (account_id,user_id) UNIQUE
+#
+# Foreign Keys
+#
+#  fk_rails_...  (account_id => accounts.id)
+#  fk_rails_...  (user_id => users.id)
+#
+
+class AccountUser < ApplicationRecord
+  belongs_to :account
+  belongs_to :user
+  belongs_to :inviter, class_name: 'User', optional: true
+
+  enum role: { agent: 0, administrator: 1 }
+  accepts_nested_attributes_for :account
+
+  after_create :create_notification_setting
+  after_destroy :destroy_notification_setting
+
+  validates :user_id, uniqueness: { scope: :account_id }
+
+  def create_notification_setting
+    setting = user.notification_settings.new(account_id: account.id)
+    setting.selected_email_flags = [:conversation_assignment]
+    setting.save!
+  end
+
+  def destroy_notification_setting
+    setting = user.notification_settings.new(account_id: account.id)
+    setting.destroy!
+  end
+end