Metadata: Add support for Registration Information

Add functionality to the MetadataGenerationService to emit Registration
and Publishing Information (RPI) as requested in the eduGAIN metadata
profile.

This functionality is controlled by these configuration variables (with
sample values):

config.aaf.fr.metadata.registrationAuthority = "https://www.federation.org/"
config.aaf.fr.metadata.registrationPolicy = "https://www.federation.org/RegistrationPolicy/"
config.aaf.fr.metadata.registrationPolicyLang = "en"

Without these values set (which is the default), this functionality is
not active.

The sample configuration file fr-config.groovy.example has sample
configuration which is commented out by default.

The MetadataGenerationService pulls this information from the config and
stores this cached locally (can be refreshed with a call to
initializeRegInfoConfig() which is otherwise called only the first time
these settings are accessed).

There is a corresponding test in MetadataGenerationServiceSpec with
expected output in testvalidentitiesdescriptorwreginfo.xml