fix(ui): basePath not handled for logout route (#6817)

## Description

Fixes an issue where if you define a `basePath` in your `next` config,
the logout button would redirect you to `/admin/logout` instead of
`/basePath/admin/logout` causing a 404.

- [x] I have read and understand the
[CONTRIBUTING.md](https://github.com/payloadcms/payload/blob/main/CONTRIBUTING.md)
document in this repository.

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)

## Checklist:

- [x] Existing test suite passes locally with my changes

packages/ui/src/elements/Logout/index.tsx

@@ -22,13 +22,15 @@ const DefaultLogout: React.FC<{
     routes: { admin },
   } = config
 
+  const basePath = process.env.NEXT_BASE_PATH ?? ''
+
   const LinkElement = Link || 'a'
 
   return (
     <LinkElement
       aria-label={t('authentication:logOut')}
       className={`${baseClass}__log-out`}
-      href={`${admin}${logoutRoute}`}
+      href={`${basePath}${admin}${logoutRoute}`}
       tabIndex={tabIndex}
     >
       <LogOutIcon />