Allow mapping user attributes when federating users through brokering

In order to provide a better experience when mapping user attributes from identity providers, Keycloak should allow mapping the attributes based on the user profile configuration.

This mapper should be able to:

• List the available attributes from the user profile configuration and respecting their permissions
• Suggest as the Claim the name of the attribute with the option to change it.

Today, we have the `Attribute Importer` mapper that forces administrators to type the name of the user attribute. Perhaps, we can introduce a new property to select attributes from the user profile configuration.