doc: add upgrade documentation

Author: omrozowicz-splunk

charts/splunk-connect-for-snmp/templates/mongodb-6.0-upgrade-job.yaml

@@ -26,4 +26,33 @@ If the `mongo-fcv-upgrade-to-6` job fails for any reason, there are two recovery
      db.adminCommand( { setFeatureCompatibilityVersion: "6.0" })
      ```
 
-    Replace `<mongodb-pod-id>` with the actual Pod ID of your MongoDB instance.
+    Replace `<mongodb-pod-id>` with the actual Pod ID of your MongoDB instance.
+
+
+### Upgrading SC4SNMP from 1.12.3 to 1.13.0
+
+When upgrading SC4SNMP from version `1.12.3` to `1.13.0`, the subchart version of MongoDB will be updated from `15.6.26` to `16.5.9`. This upgrade requires an increase in the MongoDB `Feature Compatibility Version (FCV)` from `6.0` to `7.0`.
+
+To facilitate this change, a new pre-upgrade job has been introduced in SC4SNMP: `mongo-fcv-upgrade-to-7`. This job automatically updates the Feature Compatibility Version on MongoDB before the installation of MongoDB version `16.5.9`.
+
+#### Pre-Upgrade Job: `mongo-fcv-upgrade-to-7`
+
+- The `mongo-fcv-upgrade-to-7` job is designed to ensure compatibility by running the FCV update prior to upgrading MongoDB.
+
+#### Handling Job Failures
+
+If the `mongo-fcv-upgrade-to-7` job fails for any reason, there are two recovery options:
+
+1. **Reinstall SC4SNMP**:
+
+    [Reinstall SC4SNMP](../../microk8s/sc4snmp-installation#restart-splunk-connect-for-snmp) with **Persistent Volume Claim (PVC) deletion**.
+
+2. **Manually Update MongoDB**:
+
+    [Update MongoDB's Feature Compatibility Version](https://www.mongodb.com/docs/manual/release-notes/6.0-upgrade-standalone/#upgrade-procedure) manually by executing the following command:
+     ```bash
+     microk8s exec -it pod/<mongodb-pod-id> -n sc4snmp mongosh
+     db.adminCommand( { setFeatureCompatibilityVersion: "7.0", confirm: true })
+     ```
+
+    Replace `<mongodb-pod-id>` with the actual Pod ID of your MongoDB instance.