feat: Link help center portal to an Inbox (#6903)

app/models/inbox.rb

@@ -23,11 +23,17 @@
 #  updated_at                    :datetime         not null
 #  account_id                    :integer          not null
 #  channel_id                    :integer          not null
+#  portal_id                     :bigint
 #
 # Indexes
 #
 #  index_inboxes_on_account_id                   (account_id)
 #  index_inboxes_on_channel_id_and_channel_type  (channel_id,channel_type)
+#  index_inboxes_on_portal_id                    (portal_id)
+#
+# Foreign Keys
+#
+#  fk_rails_...  (portal_id => portals.id)
 #
 
 class Inbox < ApplicationRecord
@@ -45,6 +51,7 @@ class Inbox < ApplicationRecord
   validate :ensure_valid_max_assignment_limit
 
   belongs_to :account
+  belongs_to :portal, optional: true
 
   belongs_to :channel, polymorphic: true, dependent: :destroy
 

app/models/portal.rb

@@ -37,6 +37,7 @@ class Portal < ApplicationRecord
            dependent: :nullify,
            source: :user
   has_one_attached :logo
+  has_many :inboxes, dependent: :nullify
 
   before_validation -> { normalize_empty_string_to_nil(%i[custom_domain homepage_link]) }
   validates :account_id, presence: true