Add support to mention priorityClassName for Fission components (#2254)

In Fission CI as well in a couple of scenarios, noticed Fission pods
getting preempted when Function pods are getting created. As both
Fission components and function pods have the same priority class
fission component pods might get preempted. It to be recommended to
set higher priority class for components such as Fission router, executor,
controller so that Fission functioning doesn't get disrupted.
Most of the Fission components work fine with restart except the executor. So
user should set priorityClass for Fission executor.

Signed-off-by: Sanket Sudake <sanketsudake@gmail.com>

charts/fission-all/templates/controller/deployment.yaml

@@ -66,6 +66,9 @@ spec:
       - name: config-volume
         configMap:
           name: feature-config
+{{- if .Values.priorityClassName }}
+      priorityClassName: {{ .Values.priorityClassName }}
+{{- end }}
 {{- if .Values.extraCoreComponentPodConfig }}
 {{ toYaml .Values.extraCoreComponentPodConfig | indent 6 -}}
 {{- end }}