Handle common argument in aggregate parameter for vyos module (#28182)

* Handle common agrument in aggregate parameter for vyos module

*  Add supoort to set parameter in aggregate to it's respctive
   top level argument if value not provided in aggregate.
*  Aggregate argument spec validation
*  Documentation for aggregate

* Fix unit test failure

lib/ansible/modules/network/interface/net_linkagg.py

@@ -70,6 +70,18 @@ EXAMPLES = """
     name: bond0
     state: absent
 
+- name: Create aggregate of linkagg definitions
+  net_linkagg:
+    aggregate:
+        - { name: bond0, members: [eth1] }
+        - { name: bond1, members: [eth2] }
+
+- name: Remove aggregate of linkagg definitions
+  net_linkagg:
+    aggregate:
+      - name: bond0
+      - name: bond1
+    state: absent
 """
 
 RETURN = """