Add global for image registry (#201)

This patch enables a user to override all image registry settings all at
once to point to their own registry to enable easy custom mirrors.

partially implements: https://github.com/spiffe/helm-charts/issues/139

---------

Signed-off-by: Kevin Fox <[email protected]>
Co-authored-by: Marco Franssen <[email protected]>

charts/spire/charts/spire-agent/templates/daemonset.yaml

@@ -38,7 +38,7 @@ spec:
           # This is a small image with wait-for-it, choose whatever image
           # you prefer that waits for a service to be up. This image is built
           # from https://github.com/vishnubob/wait-for-it
-          image: {{ template "spire-lib.image" .Values.waitForIt }}
+          image: {{ template "spire-lib.image" (dict "image" .Values.waitForIt.image "global" .Values.global) }}
           imagePullPolicy: {{ .Values.waitForIt.image.pullPolicy }}
           args: ["-t", "30", "-h", "{{ include "spire-agent.server-address" . | trim }}", "-p", {{ .Values.server.port | quote }}]
           resources:
@@ -48,7 +48,7 @@ spec:
         {{- end }}
       containers:
         - name: {{ .Chart.Name }}
-          image: {{ template "spire-lib.image" (dict "appVersion" $.Chart.AppVersion "image" .Values.image) }}
+          image: {{ template "spire-lib.image" (dict "appVersion" $.Chart.AppVersion "image" .Values.image "global" .Values.global) }}
           imagePullPolicy: {{ .Values.image.pullPolicy }}
           args: ["-config", "/run/spire/config/agent.conf"]
           ports: