feat: Conversation update API for sla_policy_id (#8973)

- Add an endpoint for updating conversation attributes (priority / sla_policy_id )
- Swagger spec
- minor chores around the conversation API/spec

Fixes: https://linear.app/chatwoot/issue/CW-2100/feat-backend-api-to-update-the-sla-of-a-conversation

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

@@ -0,0 +1,41 @@
+require 'rails_helper'
+
+RSpec.describe 'Enterprise Conversations API', type: :request do
+  let(:account) { create(:account) }
+  let(:admin) { create(:user, account: account, role: :administrator) }
+
+  describe 'PATCH /api/v1/accounts/{account.id}/conversations/:id' do
+    let(:conversation) { create(:conversation, account: account) }
+    let(:sla_policy) { create(:sla_policy, account: account) }
+    let(:params) { { sla_policy_id: sla_policy.id } }
+
+    context 'when it is an authenticated user' do
+      let(:agent) { create(:user, account: account, role: :agent) }
+
+      before do
+        create(:inbox_member, user: agent, inbox: conversation.inbox)
+      end
+
+      it 'updates the conversation if you are an agent with access to inbox' do
+        patch "/api/v1/accounts/#{account.id}/conversations/#{conversation.display_id}",
+              params: params,
+              headers: agent.create_new_auth_token,
+              as: :json
+
+        expect(response).to have_http_status(:success)
+        expect(JSON.parse(response.body, symbolize_names: true)[:sla_policy_id]).to eq(sla_policy.id)
+      end
+
+      it 'throws error if conversation already has a different sla' do
+        conversation.update(sla_policy: create(:sla_policy, account: account))
+        patch "/api/v1/accounts/#{account.id}/conversations/#{conversation.display_id}",
+              params: params,
+              headers: agent.create_new_auth_token,
+              as: :json
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(JSON.parse(response.body, symbolize_names: true)[:message]).to eq('Sla policy conversation already has a different sla')
+      end
+    end
+  end
+end