chore: Enable updating conversation additional attributes (#1611)

- Enable updating additional attributes via conversation API
- Handle the case when additional_attributes is nil

Fixes: #1357

spec/controllers/api/v1/accounts/conversations_controller_spec.rb

@@ -117,6 +117,38 @@ RSpec.describe 'Conversations API', type: :request do
     end
   end
 
+  describe 'POST /api/v1/accounts/{account.id}/conversations' do
+    let(:contact) { create(:contact, account: account) }
+    let(:inbox) { create(:inbox, account: account) }
+    let(:contact_inbox) { create(:contact_inbox, contact: contact, inbox: inbox) }
+
+    context 'when it is an unauthenticated user' do
+      it 'returns unauthorized' do
+        post "/api/v1/accounts/#{account.id}/conversations",
+             params: { source_id: contact_inbox.source_id },
+             as: :json
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when it is an authenticated user' do
+      let(:agent) { create(:user, account: account, role: :agent) }
+
+      it 'creates a new conversation' do
+        allow(Rails.configuration.dispatcher).to receive(:dispatch)
+        post "/api/v1/accounts/#{account.id}/conversations",
+             headers: agent.create_new_auth_token,
+             params: { source_id: contact_inbox.source_id },
+             as: :json
+
+        expect(response).to have_http_status(:success)
+        response_data = JSON.parse(response.body, symbolize_names: true)
+        expect(response_data[:additional_attributes]).to eq({})
+      end
+    end
+  end
+
   describe 'POST /api/v1/accounts/{account.id}/conversations/:id/toggle_status' do
     let(:conversation) { create(:conversation, account: account) }