VCR: Enable searching for credential types

When searching for credentials (SearchVCs()) the type field is used for determining which fields are to be included in the search, but they're not filtered on. This might make sense from JSON-LD point of view, since the query could be;

Give me credentials issued to `<DID>` with `organization.name=<name>` and `organization.city=<city>`

But the functionality is not used as such; it is used to find credentials of specific types, e.g. NutsOrganizationCredential for your own customer administration, addressbook functionality or NutsAuthorizationCredential for finding which credential(s) can be used to get access to remote data. It's also a potential vulnerability, since other credential types could unknowingly be seen as another credential.

Thus, we should also filter on credential types.

Note: that would disable a use case like "give me any credential with X=Y", but I'm not sure it's used that way atm, workaround would be multiple queries.

Start at the SearchVCs() entry point and trace how the type field currently contributes to credential searches. Review the issue discussion, then verify that results are filtered by the requested credential types and that the behavior for searches without a type is explicitly resolved.