Add back UPGRADING.md entry that was accidentally removed

UPGRADING.md

@@ -73,6 +73,38 @@ ERROR: INSTALLATION FAILED: failed post-install: warning: Hook post-install splu
 * Internal error occurred: failed calling webhook "minstrumentation.kb.io": failed to call webhook: Post "https://splunk-otel-collector-operator-webhook.default.svc:443/mutate-opentelemetry-io-v1alpha1-instrumentation?timeout=10s": dial tcp X.X.X.X:443: connect: connection refused
 ```
 
+## 0.105.5 to 0.108.0
+
+We've simplified the Helm chart configuration for `operator` auto-instrumentation.
+The values previously under `.Values.operator.instrumentation.spec.*` have been moved to `.Values.instrumentation.*`.
+
+- **No Action Needed**: If you have no customizations under `.Values.operator.instrumentation.spec.*`, no migration is required.
+- **Action Required**: Continuing to use the old values path will result in a Helm install or upgrade error, blocking the process.
+
+Migration Steps:
+
+1. **Find** any references to `.Values.operator.instrumentation.spec.*` in your Helm values with custom values.
+2. **Migrate** them from `.Values.operator.instrumentation.spec.*` to `.Values.instrumentation.*`.
+
+Example Migration:
+
+Before (Deprecated Path):
+
+```yaml
+operator:
+  instrumentation:
+    spec:
+      endpoint: XXX
+      ...
+```
+
+After (Updated Path):
+```yaml
+instrumentation:
+  endpoint: XXX
+  ...
+```
+
 ## 0.105.3 to 0.105.4
 
 The `Java instrumentation` for Operator auto-instrumentation has been upgraded from v1.32.2 to v2.7.0.