Modify rule S117: Add exception to kubernetes language (#4558)

rules/S117/kubernetes/rule.adoc

@@ -2,12 +2,24 @@
 :identifier: local variable and function parameter
 :identifier_plural: local variables and function parameters
 :identifier_or: local variable or function parameter
-:regex: ^[a-z][a-zA-Z0-9]*$
+:regex: ^\$[a-z][a-zA-Z0-9]*$
 
-include::../rule.adoc[]
+
+include::../introduction.adoc[]
+
+include::../why-is-this-an-issue.adoc[]
+
+=== Exceptions
+
+The rule does not raise an issue on the usages of the blank identifier `$_` or the root context `$`.
+
+include::../what-is-the-potential-impact.adoc[]
+
+include::../how-to-fix-it.adoc[]
 
 As a default, we suggest using the camelCase naming convention, as this is widely adopted for variables in Helm.
 
+
 === Code examples
 
 ==== Noncompliant code example
@@ -51,11 +63,20 @@ data:
   {{ $keyC }}: {{ $valC | quote }}
   {{- end }}
 ----
+
+[source,text]
+----
+# Usage of blank identifier
+{{- $_ := set .Values.ingress.annotations "kubernetes.io/ingress.class" .Values.ingress.className -}}
+
+# Usage of root context
+{{- $ := . -}}
+----
 == Resources
 
 === Documentation
 
-
+* Helm documentation - https://helm.sh/docs/chart_template_guide/variables/[Helm - Variables]
 * Go documentation - https://go.dev/doc/effective_go#names[Effective Go - Names]
 * Wikipedia - https://en.wikipedia.org/wiki/Naming_convention_(programming)[Naming Convention (programming)]