fix(sizer): 🐛 make GARM env vars conditional in receiver deployment

Clusters without GARM lack the garm-fixed-credentials secret, causing
pod crash loops. The receiver already handles empty GARM_URL gracefully.

Ref: IPCEICIS-6886

template/stacks/ci-sizer/sizer-receiver/deployment.yaml

@@ -39,15 +39,17 @@ spec:
                 secretKeyRef:
                   name: sizer-tokens
                   key: hmac-key
+{{{ if .Env.GARM_URL }}}
             - name: GARM_URL
-              value: "http://garm.garm.svc.cluster.local:80"
+              value: "{{{ .Env.GARM_URL }}}"
             - name: GARM_USER
-              value: "admin"
+              value: "{{{ .Env.GARM_USER }}}"
             - name: GARM_PASSWORD
               valueFrom:
                 secretKeyRef:
                   name: garm-fixed-credentials
                   key: admin_password
+{{{ end }}}
             - name: RECEIVER_OIDC_ISSUER
               value: "https://dex.{{{ .Env.DOMAIN }}}"
             - name: RECEIVER_OIDC_CLIENT_ID