Replace Eureka service discovery with an application service

[punycode]

CoffeeNet currently utilizes Eureka to discover CoffeeNet applications in the eco-system and also decide, which applications CoffeeNet users can access. This approach has several short-comings:

• Coupling of applications discovery to a specific service-discovery mechanism
• Not flexible the way it is done, solely relying on global roles for what applications are accessible
• Eureka-specific, therefore not allowing for different approaches to propagating service discovery (like K8S, AMQP, etc.)
• Eureka and the Netflix stack in general becoming slowly deprecated on Spring Boot
• Health of applications bound to the health of the discovery service

Proposal:

• Create API for CoffeeNet application discovery in a new service
  • don't reuse the coffeenet-discovery project, it is something different
  • authenticated API, returning registered applications for the user
  • support multiple mechanisms for actual application discovery
  • K8S API
  • AMQP
  • OIDC scopes
  • etc.
  • support more fine-grained mechanism for application accessability decision
  • Application-level RBAC
  • ABAC
  • etc.
• Migrate the user facing parts of the application discovery (coffeenet-navigationbar) to query the service instead of being populated by Eureka
• Sunset coffeenet-discovery

[punycode]

Will be addressed later, see #69