Fix MergeConfigs() to work with multiple node pools (#1059)

### Description
Fix MergeConfigs() to work with multiple node pools

### Issues Resolved
Fixes #1057 

### Check List
- [x] Commits are signed per the DCO using --signoff 
- [x] Unittest added for the new/changed functionality and all unit
tests are successful
- [x] Customer-visible features documented
- [x] No linter warnings (`make lint`)

If CRDs are changed:
- [x] CRD YAMLs updated (`make manifests`) and also copied into the helm
chart
- [x] Changes to CRDs documented

Please refer to the [PR
guidelines](https://github.com/opensearch-project/opensearch-k8s-operator/blob/main/docs/developing.md#submitting-a-pr)
before submitting this pull request.

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and
signing off your commits, please check
[here](https://github.com/opensearch-project/OpenSearch/blob/main/CONTRIBUTING.md#developer-certificate-of-origin).

---------

Signed-off-by: Jim Dickinson <[email protected]>

Author: jimdickinson

opensearch-operator/pkg/helpers/helpers.go

@@ -154,13 +154,14 @@ func GetByComponent(left opsterv1.ComponentStatus, right opsterv1.ComponentStatu
 }
 
 func MergeConfigs(left map[string]string, right map[string]string) map[string]string {
-	if left == nil {
-		return right
+	result := make(map[string]string)
+	for k, v := range left {
+		result[k] = v
 	}
 	for k, v := range right {
-		left[k] = v
+		result[k] = v
 	}
-	return left
+	return result
 }
 
 // Return the keys of the input map in sorted order

opensearch-operator/pkg/helpers/helpers_test.go

@@ -1,7 +1,7 @@
 package helpers
 
 import (
-	opsterv1 "github.com/Opster/opensearch-k8s-operator/opensearch-operator/api/v1"
+  	opsterv1 "github.com/Opster/opensearch-k8s-operator/opensearch-operator/api/v1"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 	corev1 "k8s.io/api/core/v1"
@@ -133,4 +133,32 @@ var _ = Describe("Helper Functions", func() {
 			})
 		})
 	})
+
+  Describe("MergeConfigs mutation behavior", func() {
+    It("should merge the maps such that right is higher priority than left, and not mutate either argument when merging", func() {
+      generalConfig := map[string]string{"http.compression": "true"}
+      poolConfig := map[string]string{"node.data": "false"}
+
+      // Save a copy of the original
+      original := map[string]string{"http.compression": "true"}
+
+      // Merge and check result
+      merged := MergeConfigs(generalConfig, poolConfig)
+      expected := map[string]string{"http.compression": "true", "node.data": "false"}
+      Expect(merged).To(Equal(expected))
+
+      // Check that longLived was not mutated
+      Expect(generalConfig).To(Equal(original))
+
+      // Merge again with a new config
+      poolConfig2 := map[string]string{"node.master": "false", "http.compression": "false"}
+      expected2 := map[string]string{"http.compression": "false", "node.master": "false"}
+      merged2 := MergeConfigs(generalConfig, poolConfig2)
+      Expect(merged2).To(Equal(expected2))
+
+      // Still not mutated
+      Expect(generalConfig).To(Equal(original))
+    })
+  })
+ 
 })