v2.0.0: Katsu UUIDs, completeness stats

What's Changed

• DIG-1240: API middleware service to handle queries across federated instances by @OrdiNeu in #1
• Fix to the age at diagnosis summary stat not working by @OrdiNeu in #4
• Completeness stats query by @OrdiNeu in #2
• Fix an issue where an unknown date of birth or diagnosis would fail by @OrdiNeu in #5

Full Changelog: v1.0.0...v2.0.0