[WIP] authenticated microservices

[petertrr]

• Make default HttpSecurityChain have lowest precedence, because it captures all endpoints (/**) and more specific matchers should be able to override it by using higher precedence. Make ConvertingAuthenticationManager primary bean to avoid conflict when autowiring by type
• App-to-app authentication using ServiceAccount tokens (similarly to this authentication mode of Vault)
  • Add a ServiceAccount microservice-sa for all microservices; mount its token as a projected volume
  • Add a WebClientCustomizer to add this token as a custom header; token is updated every 5 minutes
  • Add spring-security components to authorize request based on the service account token
  • Add SA-based authentication for /internal endpoints of backend and for orchestartor and sandbox
• Switch spring-cloud-kubernetes implementation from kubernetes-client to fabric8-client in save-backend
• Enable loading ConfigMaps using spring-cloud-kubernetes integration (for some reason resolving ${spring.datasource.backend-url} won't work with existing loading of optional properties file)

Part of #1049