Add support for FIDO Convenience MDS

[MasterKale]

This PR updates MetadataService to support the FIDO Convenience Metadata Service. This service provides localized names and light and dark iconography for credential providers, keyed by the AAGUID they return from WebAuthn .create() calls. This service is intended to help Relying Parties display user-friendly names and icons in RP user self management portals when displaying a user's passkeys.

By default, a bare call to MetadataService.initialize() will now automatically query the FIDO Alliance's official service at https://c-mds.fidoalliance.org. Similar to existing FIDO MDS configuration, two new arguments have been added to initialize():

• convenienceMDSServers is an array of URLs to Convenience MDS services
• conveniencePayloads is an array of locally cached JSON payloads that would otherwise be downloaded from a Convenience MDS service

An AAGUID can be passed into the new MetadataService.getProviderMetadata() method to get the corresponding localized names and icons for that credential provider.

TODO

• Additionally, verifyRegistrationResponse() will automatically include matching provider metadata when MetadataService has been initialized and an AAGUID is recognized.

Fixes #743.