Missing 'provider-id' in cloudservices documents

[Nicolas Bock]

When scaling some charms, documents with empty provider-id fields are created.

Reproducer

Using juju-2.9.47:

```
juju deploy minio
juju deploy argo-server
juju deploy argo-controller
juju deploy kfp-schedwf
juju deploy kfp-viewer
juju relate argo-controller minio
```

At this point only the minio charm has a document in the cloudservices collection:

```
juju:PRIMARY> db.cloudservices.find({"_id": {$regex: "53836"}}, {"_id": true, "provider-id": true})
{ "_id" : "53836ccf-d6cf-4a35-8074-cdf8cb94fcdd:a#minio", "provider-id" : "6bd580b3-ec38-4a25-ac21-7800f9dcc0a2" }
```

Scale the applications:

```
juju add-unit argo-controller
juju add-unit argo-server
juju add-unit kfp-schedwf
juju add-unit kfp-viewer
```

```
juju:PRIMARY> db.cloudservices.find({"_id": {$regex: "53836"}}, {"_id": true, "provider-id": true})
{ "_id" : "53836ccf-d6cf-4a35-8074-cdf8cb94fcdd:a#argo-controller", "provider-id" : "" }
{ "_id" : "53836ccf-d6cf-4a35-8074-cdf8cb94fcdd:a#argo-server", "provider-id" : "" }
{ "_id" : "53836ccf-d6cf-4a35-8074-cdf8cb94fcdd:a#kfp-schedwf", "provider-id" : "" }
{ "_id" : "53836ccf-d6cf-4a35-8074-cdf8cb94fcdd:a#kfp-viewer", "provider-id" : "" }
{ "_id" : "53836ccf-d6cf-4a35-8074-cdf8cb94fcdd:a#minio", "provider-id" : "6bd580b3-ec38-4a25-ac21-7800f9dcc0a2" }
```

These documents persits even after scaling the applications back down to 1 unit:

```
juju remove-unit --num-units 1 argo-controller
juju remove-unit --num-units 1 argo-server
juju remove-unit --num-units 1 kfp-viewer
juju remove-unit --num-units 1 kfp-schedwf
```

[Ian Booth (wallyworld)]

As an aside, the "cloud services" records are associated with the application (and specifically the k8s service resource), so are expected to persist for the life of the application in the juju model.