Add likes model, controller and tests

app/models/post.rb

@@ -2,6 +2,7 @@ class Post < ApplicationRecord
   belongs_to :board
   belongs_to :user
   belongs_to :post_status, optional: true
+  has_many :likes, dependent: :destroy
   has_many :comments, dependent: :destroy
 
   validates :title, presence: true, length: { in: 4..64 }