[vpc] Give predictable name to subnet configmap (#1590)

## What this PR does

The new VPC feature creates a configmap, containing the list of subnets
under the VPC. However, the configmap has the VPC ID in its name, rather
than the name of the VPC, making it harder to target inside the
dashboard, as the helper functions from Helm (e.g. sha256sum) may not be
available in the dashboard's custom resources. This patch renames the
configmap to use the VPC's name.

### Release note

```release-note
[vpc] Change the subnet configmap name to a human-friendly value
(matching the VPC name), instead of being derived via a sha256sum,
making it easier to reference in the dashboard.
```

packages/apps/vpc/templates/vpc.yaml

@@ -58,9 +58,9 @@ spec:
 apiVersion: v1
 kind: ConfigMap
 metadata:
-  name: {{ $vpcId }}-subnets
+  name: {{ $.Release.Name }}-subnets
   labels:
-    cozystack.io/vpcName: {{ $.Release.Name }}
+    cozystack.io/vpcId: {{ $vpcId }}
     cozystack.io/tenantName: {{ $.Release.Namespace }}
 data:
   subnets: |