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

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

test/integration/targets/iosxr_logging/tests/cli/basic.yaml

@@ -100,11 +100,26 @@
       - 'result.changed == true'
       - '"logging buffered 4800000" in result.commands'
 
+- name: Change logging parameters using aggregate
+  iosxr_logging:
+    aggregate:
+      - { dest: console, level: notifications }
+      - { dest: buffered, size: 4700000 }
+    provider: "{{ cli }}"
+  register: result
+
+- assert:
+    that:
+      - 'result.changed == true'
+      - '"logging buffered 4700000" in result.commands'
+      - '"logging console notifications" in result.commands'
+
 - name: remove logging as collection tearDown
   iosxr_logging:
     aggregate:
-      - { dest: console, level: warning, state: absent }
-      - { dest: buffered, size: 4800000, state: absent }
+      - { dest: console, level: notifications }
+      - { dest: buffered, size: 4700000 }
+    state: absent
     provider: "{{ cli }}"
   register: result