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/folder.rb

@@ -0,0 +1,20 @@
+# == Schema Information
+#
+# Table name: kbase_folders
+#
+#  id          :bigint           not null, primary key
+#  name        :string
+#  created_at  :datetime         not null
+#  updated_at  :datetime         not null
+#  account_id  :integer          not null
+#  category_id :integer          not null
+#
+class Kbase::Folder < ApplicationRecord
+  belongs_to :account
+  belongs_to :category
+  has_many :articles, dependent: :nullify
+
+  validates :account_id, presence: true
+  validates :category_id, presence: true
+  validates :name, presence: true
+end