ref(monitors): Add beta pill (#41295)

Add the beta pill

ex:
<img width="208" alt="image"
src="https://user-images.githubusercontent.com/9372512/201442444-9cc23309-f817-431c-b8b4-53ec2a94d018.png">

static/app/components/sidebar/index.tsx

@@ -235,6 +235,7 @@ function Sidebar({location, organization}: Props) {
         label={t('Monitors')}
         to={`/organizations/${organization.slug}/monitors/`}
         id="monitors"
+        isBeta
       />
     </Feature>
   );