When set for an export config, if the user doesn't have that attribute, their email will be substituted as a default. If any of the values is not a valid email address, they are filtered out.
Closes#29
* simplify AttributeEndpointsResourceProvider
* improve explanation of properties in AdminUiPage
* add example for mailing lists and map endpoint
* better explain configuration and operation of provider in main readme
* adjust the Keycloak realm
* Add unit test for endpoint class
Adds an endpoint that returns the list of attribute values as a map of attribute names in the requested attribute group.
This is useful for requesting the mailing list addresses, where the individual attributes apply to different mailing lists.
getRoleMembersStream only returns users with the role assigned
directly, so exported attributes silently excluded users who have
matchRole via group membership. Filter all realm users with
hasRole() instead, matching the resolution already used for authRole.
