new group processor based on attribute

[howkymike]

Default attribute name: alfrescoGroupName To make it work I deleted groupProperties.put(ContentModel.PROP_AUTHORITY_NAME, groupName); from KeycloakUserRegistry.java

[AFaust]

Note: The "wontfix" label applies to the specific way the change in this PR is done, not to the idea behind it. As outlined in #18 I plan to work on a flexible attribute mapping scheme (for users and groups), and will likely combine this with a configuration flag that would allow those mappings to specify the Alfresco authority name. For the sake of guarding against accidental duplicates, the default will remain that the ID is used for the name, but admins will then have a choice to change that behaviour.

Thanks @howkymike for providing the change so anyone interested in this have a starting point to use this until I have made the above available.