refactor: rename _getKeyValue.tpl to _getKeyLookup.tpl and add detailed function documentation

On-behalf-of: @SAP angel.kafazov@sap.com
Signed-off-by: Angel Kafazov <akafazov@cst-bg.net>

Author: akafazov

charts/common/templates/_getKeyValue.tpl charts/common/templates/_getKeyLookup.tpl

@@ -1,3 +1,27 @@
+{{/* 
+  Function: common.getKeyValue
+  Description: 
+    Retrieves a value from the Helm chart's values.yaml file based on a prioritized key lookup.
+    The function searches for a value in the following order:
+      1. An override key (`keyPathOverride`).
+      2. A global key (`global.keyPath`).
+      3. A default key (`defaults.keyPath`).
+    If none of these keys exist, it returns an empty string.
+
+  Parameters:
+    - .key: The path to the key being retrieved.
+    - .Values: The values object passed to the Helm template.
+
+  Dependencies:
+    - Uses helper functions "common.hasNestedKey" and "common.getNestedValue" to check 
+      the existence of nested keys and retrieve their values.
+
+  Usage:
+    This function is intended to prioritize overrides and global configurations 
+    in a Helm chart's values.yaml file while providing default fallback values.
+
+*/}}
+
 {{- define "common.getKeyValue" -}}
   {{- $keyPath := .key -}}
   {{- $values := .Values -}}