Extend MinimalPermissionsPlugin to support delegated and application permissions

[waldekmastykarz]

Extend MinimalPermissionsPlugin to support delegated and application permissions. To do this, we need to introduce a new property named schemeName. If specified, the plugin retrieves scopes from that scheme. If not specified, plugin reads information from the first oauth2 scheme in the spec, like it does now.

We need this to allow discovering minimal permissions for delegated and application permissions which are specified in the API spec in separate schemes.