Changes:
- Hazelcast is the storage provider of the Registry Map. You are able to start many spring-boot-admin instances and they build a distributed cache cluster. Hazelcast can be configured via the application.yaml config file.
- The Registry API is more "Restful". RegisterApplication returns HTTP Code 201 "Created" and a location field now. UnregisterApplication and UnregisterAllApplications returns HTTP Code 204 "No Content". The API is documented via Swagger.
- The Application domain model is immutable and can be build via the Builder pattern.
- The spring-boot-admin-server module contains many new Integration Tests.
- Correct Spring REST exception handling was added. All Spring exceptions are translated to the correct HTTP Codes now. A new "ApplicationNotFound" exception was introduced.