chore: handle old events in cluster

Signed-off-by: Tanisha goyal <tanishag@nvidia.com>

Author: tanishagoyal2

docs/designs/025-processing-strategy-for-health-checks.md

@@ -532,6 +532,8 @@ func createPipeline() interface{} {
 
 Update the default pipeline query to exclude `processingStrategy=STORE_ONLY` events. We need this condition for every rule that's why we are adding it at code level instead of keeping it at config file level.
 
+**Backward Compatibility Note:** Historical events in the database (created before this feature) won't have the `processingstrategy` field. These old events should be treated as `EXECUTE_REMEDIATION` (they were meant to be processed). We use `$or` to explicitly match both `EXECUTE_REMEDIATION` and a missing field to ensure backward compatibility. Other modules and health monitors do not require changes since they only act on newly inserted events, which will already have the `processingStrategy` field set (all health monitors run in `EXECUTE_REMEDIATION` mode by default). 
+
 File: `health-events-analyzer/pkg/reconciler/reconciler.go`
 
 ```go
@@ -542,11 +544,18 @@ func (r *Reconciler) getPipelineStages(
 	// CRITICAL: Always start with agent filter to exclude events from health-events-analyzer itself
 	// This prevents the analyzer from matching its own generated events, which would cause
 	// infinite loops and incorrect rule evaluations
+	//
+	// Backward Compatibility: Use $or to include events where processingstrategy is either
+	// EXECUTE_REMEDIATION or missing (old events created before this feature was added).
+	// Old events without this field should be treated as EXECUTE_REMEDIATION.
 	pipeline := []map[string]interface{}{
 		{
 			"$match": map[string]interface{}{
-				"healthevent.agent":  map[string]interface{}{"$ne": "health-events-analyzer"},
-				"healthevent.processingstrategy": map[string]interface{}{"$eq": "EXECUTE_REMEDIATION"}, // Exclude STORE_ONLY by default
+				"healthevent.agent": map[string]interface{}{"$ne": "health-events-analyzer"},
+				"$or": []map[string]interface{}{
+					{"healthevent.processingstrategy": "EXECUTE_REMEDIATION"},
+					{"healthevent.processingstrategy": map[string]interface{}{"$exists": false}},
+				},
 			},
 		},
 	}