scope annotation should be `sealedsecrets.bitnami.com/scope`

It doesn't make sense to combine the following annotations:

```
sealedsecrets.bitnami.com/cluster-wide
sealedsecrets.bitnami.com/strict
sealedsecrets.bitnami.com/namespace-wide
```

so the annotation for this should really be:

```
sealedsecrets.bitnami.com/scope
```

with the possible values being `cluster-wide`, `strict`, `namespace-wide`

Start by locating where the sealed-secrets controller handles the cluster-wide, strict, and namespace-wide annotations. Check how those values are documented and tested, then determine whether the proposed scope annotation can replace them consistently. Done means the supported annotation is sealedsecrets.bitnami.com/scope with the three stated values and the old combination is no longer required.

Written by the indexing model from the issue text.