Helm-Toolkit: update K8S resources function

This PS updates the K8s pod resources function to both include
basic documentation, and also allow null values to be used if
no resource request or limit is desired.

Change-Id: I9dee6af1167a12f0c22b368220ca6343a8c6dc73
Signed-off-by: Pete Birley <pete@port.direct>

helm-toolkit/templates/snippets/_kubernetes_resources.tpl

@@ -14,16 +14,55 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */}}
 
+{{/*
+abstract: |
+  Renders kubernetes resource limits for pods
+values: |
+  pod:
+    resources:
+      enabled: true
+      api:
+        requests:
+          memory: "128Mi"
+          cpu: "100m"
+        limits:
+          memory: "1024Mi"
+          cpu: "2000m"
+
+usage: |
+  {{ include "helm-toolkit.snippets.kubernetes_resources" ( tuple . .Values.pod.resources.api ) }}
+return: |
+  resources:
+    limits:
+      cpu: "2000m"
+      memory: "1024Mi"
+    requests:
+      cpu: "100m"
+      memory: "128Mi
+*/}}
+
 {{- define "helm-toolkit.snippets.kubernetes_resources" -}}
 {{- $envAll := index . 0 -}}
 {{- $component := index . 1 -}}
 {{- if $envAll.Values.pod.resources.enabled -}}
 resources:
+  {{- if or $component.limits.cpu $component.limits.memory }}
   limits:
+    {{- if $component.limits.cpu }}
     cpu: {{ $component.limits.cpu | quote }}
+    {{- end }}
+    {{- if $component.limits.memory }}
     memory: {{ $component.limits.memory | quote }}
+    {{- end }}
+  {{- end }}
+  {{- if or $component.requests.cpu $component.requests.memory }}
   requests:
+    {{- if $component.requests.cpu }}
     cpu: {{ $component.requests.cpu | quote }}
+    {{- end }}
+    {{- if $component.requests.memory }}
     memory: {{ $component.requests.memory | quote }}
+    {{- end }}
+  {{- end }}
 {{- end -}}
 {{- end -}}