eos aggregate spec validation and doc changes (#28414)

*  Add aggregate validation for eos DI modules
*  Doc change to add aggregate examples

lib/ansible/modules/network/layer3/net_vrf.py

@@ -51,6 +51,23 @@ EXAMPLES = """
   net_vrf:
     name: MANAGEMENT
     state: absent
+
+- name: Create aggregate of VRFs with purge
+  net_vrf:
+    aggregate:
+      - { name: test4, rd: "1:204" }
+      - { name: test5, rd: "1:205" }
+    state: present
+    purge: yes
+
+- name: Delete aggregate of VRFs
+  net_vrf:
+    aggregate:
+      - name: test2
+      - name: test3
+      - name: test4
+      - name: test5
+    state: absent
 """
 
 RETURN = """