Fix spacing issues on values.yaml file (#1812)

Helm Chart ConfigMap is using `OpenServiceMesh.serviceCertValidityDuration`
Current default values are using `OpenServiceMesh.certmanager.serviceCertValidityDuration`
Looking at the other places this is referenced I believe this should be updated to be outside of certmanager. It looks like it doesn't happen in the [osm cli](https://github.com/openservicemesh/osm/blob/11e7e5eae48790bef3c7e3a51f7d1e6206d45a0d/cmd/cli/install.go#L210) because it is passing the value itself.
[Configmap Template](https://github.com/openservicemesh/osm/blob/11e7e5eae48790bef3c7e3a51f7d1e6206d45a0d/charts/osm/templates/osm-configmap.yaml#L21):
```
service_cert_validity_duration: {{ .Values.OpenServiceMesh.serviceCertValidityDuration | quote }}
```

charts/osm/values.yaml

@@ -23,7 +23,7 @@ OpenServiceMesh:
     issuerName: osm-ca
     issuerKind: Issuer
     issuerGroup: cert-manager
-    serviceCertValidityDuration: 24h
+  serviceCertValidityDuration: 24h
   caBundleSecretName: osm-ca-bundle
   grafana:
     port: 3000