feat: Update API for contact avatar (#4719)

Added the ability to update the contact's avatar via API and Dashboard.

- Contact create and update APIs can now accept avatar attachment parameters [form data].
- Contact create and update endpoints can now accept the avatar_url parameter.[json]
- API endpoint to remove a contact avatar.
- Updated Contact create/edit UI components with avatar support

Fixes: #3428

spec/factories/contacts.rb

@@ -3,9 +3,12 @@
 FactoryBot.define do
   factory :contact do
     sequence(:name) { |n| "Contact #{n}" }
-    avatar { fixture_file_upload(Rails.root.join('spec/assets/avatar.png'), 'image/png') }
     account
 
+    trait :with_avatar do
+      avatar { fixture_file_upload(Rails.root.join('spec/assets/avatar.png'), 'image/png') }
+    end
+
     trait :with_email do
       sequence(:email) { |n| "contact-#{n}@example.com" }
     end