user: create Buildroot subclass as alias to Busybox (#83666)

Fixes: #83665

changelogs/fragments/buildroot.yml

@@ -0,0 +1,3 @@
+---
+bugfixes:
+  - user - Create Buildroot subclass as alias to Busybox (https://github.com/ansible/ansible/issues/83665).

lib/ansible/modules/user.py

@@ -3243,6 +3243,11 @@ class Alpine(BusyBox):
     distribution = 'Alpine'
 
 
+class Buildroot(BusyBox):
+    platform = 'Linux'
+    distribution = 'Buildroot'
+
+
 def main():
     ssh_defaults = dict(
         bits=0,