#474

As part of the integration with OED/DD (Digitalt dødsbo) as a new external role provider, an easy way to analyse and extract all attributeIds and values from a XacmlPolicy is needed.
This will be used to evaluate whether or not the policy contains a subject attribute for an OED/DD role code, and since it's populated to the XacmlPolicy object it will be cached along side policy itself.

The logic can later be reused by the resource-registry which will need same logic for analysing the policy for building rolecode register and required validation logic when publishing a resource.