Feature: Knowledge Base APIs (#1002)

- Introduce models & migrations for portals, categories, folders and articles
- CRUD API for portals
- CRUD API for categories

Addresses: #714

Co-authored-by: Sojan <sojan@pepalo.com>

app/models/kbase/portal.rb

@@ -0,0 +1,30 @@
+# == Schema Information
+#
+# Table name: kbase_portals
+#
+#  id            :bigint           not null, primary key
+#  account_id    :integer          not null
+#  color         :string
+#  custom_domain :string
+#  header_text   :text
+#  homepage_link :string
+#  name          :string           not null
+#  page_title    :string
+#  slug          :string           not null
+#  created_at    :datetime         not null
+#  updated_at    :datetime         not null
+#
+# Indexes
+#
+#  index_kbase_portals_on_slug  (slug) UNIQUE
+#
+class Kbase::Portal < ApplicationRecord
+  belongs_to :account
+  has_many :categories, dependent: :destroy
+  has_many :folders,  through: :categories
+  has_many :articles, dependent: :destroy
+
+  validates :account_id, presence: true
+  validates :name, presence: true
+  validates :slug, presence: true
+end