Feature: As a admin, I should be able to add webhooks to account (#572)

Co-authored-by: Pranav Raj S <pranavrajs@gmail.com>

app/models/webhook.rb

@@ -16,6 +16,7 @@ class Webhook < ApplicationRecord
   belongs_to :inbox, optional: true
 
   validates :account_id, presence: true
+  validates :url, uniqueness: { scope: [:account_id] }, format: { with: URI::DEFAULT_PARSER.make_regexp }
 
   enum webhook_type: { account: 0, inbox: 1 }
 end