iosxr modules aggregate check and other minor refactor (#28360)

*  iosxr aggregate validation
*  vyos_user, junos_user minor changes
*  Aggregated documentation

lib/ansible/modules/network/iosxr/iosxr_user.py

@@ -110,10 +110,12 @@ commands:
     - username ansible secret password group sysadmin
     - username admin secret admin
 """
-
 from functools import partial
 
+from copy import deepcopy
+
 from ansible.module_utils.basic import AnsibleModule
+from ansible.module_utils.network_common import remove_default_spec
 from ansible.module_utils.iosxr import get_config, load_config
 from ansible.module_utils.iosxr import iosxr_argument_spec, check_args
 
@@ -243,19 +245,27 @@ def map_params_to_obj(module):
 def main():
     """ main entry point for module execution
     """
-    argument_spec = dict(
-        aggregate=dict(type='list', aliases=['users', 'collection']),
+    element_spec = dict(
         name=dict(),
 
         configured_password=dict(no_log=True),
         update_password=dict(default='always', choices=['on_create', 'always']),
 
         group=dict(aliases=['role']),
-
-        purge=dict(type='bool', default=False),
         state=dict(default='present', choices=['present', 'absent'])
     )
+    aggregate_spec = deepcopy(element_spec)
+    aggregate_spec['name'] = dict(required=True)
 
+    # remove default in aggregate spec, to handle common arguments
+    remove_default_spec(aggregate_spec)
+
+    argument_spec = dict(
+        aggregate=dict(type='list', elements='dict', options=aggregate_spec, aliases=['users', 'collection']),
+        purge=dict(type='bool', default=False)
+    )
+
+    argument_spec.update(element_spec)
     argument_spec.update(iosxr_argument_spec)
     mutually_exclusive = [('name', 'aggregate')]