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

app/views/api/v1/accounts/contacts/avatar.json.jbuilder

@@ -0,0 +1,3 @@
+json.payload do
+  json.partial! 'api/v1/models/contact.json.jbuilder', resource: @contact, with_contact_inboxes: false
+end