chore: Ability to Disable Gravatars (#5027)

fixes: #3853

- Introduced DISABLE_GRAVATAR Global Config, which will stop chatwoot from making API requests to gravatar
- Cleaned up avatar-related logic and centralized it into the avatarable concern
- Added specs for the missing cases
- Added migration for existing installations to move the avatar to attachment, rather than making the API that results in 404.

spec/models/concerns/avatarable_shared.rb

@@ -0,0 +1,41 @@
+require 'rails_helper'
+
+shared_examples_for 'avatarable' do
+  let(:avatarable) { create(described_class.to_s.underscore) }
+
+  it { is_expected.to have_one_attached(:avatar) }
+
+  it 'add avatar_url method' do
+    expect(avatarable.respond_to?(:avatar_url)).to be true
+  end
+
+  context 'when avatarable has an email attribute' do
+    it 'enques job when email is changed on avatarable create' do
+      avatarable = build(described_class.to_s.underscore, account: create(:account))
+      if avatarable.respond_to?(:email)
+        avatarable.email = 'test@test.com'
+        avatarable.skip_reconfirmation! if avatarable.is_a? User
+        expect(Avatar::AvatarFromGravatarJob).to receive(:set).with(wait: 30.seconds).and_call_original
+      end
+      avatarable.save!
+      expect(Avatar::AvatarFromGravatarJob).to have_been_enqueued.with(avatarable, avatarable.email) if avatarable.respond_to?(:email)
+    end
+
+    it 'enques job when email is changes on avatarable update' do
+      if avatarable.respond_to?(:email)
+        avatarable.email = 'xyc@test.com'
+        avatarable.skip_reconfirmation! if avatarable.is_a? User
+        expect(Avatar::AvatarFromGravatarJob).to receive(:set).with(wait: 30.seconds).and_call_original
+      end
+      avatarable.save!
+      expect(Avatar::AvatarFromGravatarJob).to have_been_enqueued.with(avatarable, avatarable.email) if avatarable.respond_to?(:email)
+    end
+
+    it 'will not enqueu when email is not changed on avatarable update' do
+      avatarable.updated_at = Time.now.utc
+      expect do
+        avatarable.save!
+      end.not_to have_enqueued_job(Avatar::AvatarFromGravatarJob)
+    end
+  end
+end