Meraki scenario guide - describe how to merge new data with old data (#48999)

* Described how to merge new data with old data in the Meraki guide
Co-Authored-By: kbreit <kevin.breit@kevinbreit.net>

docs/docsite/rst/scenario_guides/guide_meraki.rst

@@ -124,6 +124,67 @@ Handling Returned Data
 
 Since Meraki's response data uses lists instead of properly keyed dictionaries for responses, certain strategies should be used when querying data for particular information. For many situations, use the ``selectattr()`` Jinja2 function.
 
+Merging Existing and New Data
+=============================
+
+Ansible's Meraki modules do not allow for manipulating data. For example, you may need to insert a rule in the middle of a firewall ruleset. Ansible and the Meraki modules lack a way to directly merge to manipulate data. However, a playlist can use a few tasks to split the list where you need to insert a rule and then merge them together again with the new rule added. The steps involved are as follows:
+
+1. Create blank "front" and "back" lists.
+    ::
+
+        vars:
+          - front_rules: []
+          - back_rules: []
+2. Get existing firewall rules from Meraki and create a new variable.
+    ::
+
+        - name: Get firewall rules
+          meraki_mx_l3_firewall:
+            auth_key: abc123
+            org_name: YourOrg
+            net_name: YourNet
+            state: query
+          delegate_to: localhost
+          register: rules
+        - set_fact:
+            original_ruleset: '{{rules.data}}'
+3. Write the new rule. The new rule needs to be in a list so it can be merged with other lists in an upcoming step. The blank `-` puts the rule in a list so it can be merged.
+    ::
+
+        - set_fact:
+            new_rule:
+              - 
+                - comment: Block traffic to server
+                  src_cidr: 192.0.1.0/24
+                  src_port: any
+                  dst_cidr: 192.0.1.2/32
+                  dst_port: any
+                  protocol: any
+                  policy: deny
+4. Split the rules into two lists. This assumes the existing ruleset is 2 rules long.
+    ::
+
+        - set_fact:
+            front_rules: '{{front_rules + [ original_ruleset[:1] ]}}'
+        - set_fact:
+            back_rules: '{{back_rules + [ original_ruleset[1:] ]}}'
+5. Merge rules with the new rule in the middle.
+    ::
+
+        - set_fact:
+            new_ruleset: '{{front_rules + new_rule + back_rules}}'
+6. Upload new ruleset to Meraki.
+    ::
+
+        - name: Set two firewall rules
+          meraki_mx_l3_firewall:
+            auth_key: abc123
+            org_name: YourOrg
+            net_name: YourNet
+            state: present
+            rules: '{{ new_ruleset }}'
+          delegate_to: localhost
+
 Error Handling
 ==============