== does application-prod.yaml win? ==

demo.datasource-url is set in application.yaml and again in application-prod.yaml.

--- 1. prod profile active, no environment variable ---
$ java -jar target/profiles-and-config-1.0.0.jar --spring.profiles.active=prod
  active profiles : prod, prod-db, prod-metrics
  effective value : jdbc:postgresql://prod-db:5432/orders
    1. jdbc:postgresql://prod-db:5432/orders <- 'file application-prod.yaml' via location 'optional:classpath:/''}
    2. jdbc:h2:mem:default                <- 'file application.yaml' via location 'optional:classpath:/''}
  holders that lost: 1

--- 2. identical, plus one leftover environment variable ---
$ DEMO_DATASOURCE_URL=jdbc:postgresql://leftover:5432/orders \
    java -jar target/profiles-and-config-1.0.0.jar --spring.profiles.active=prod
  active profiles : prod, prod-db, prod-metrics
  effective value : jdbc:postgresql://leftover:5432/orders
    1. jdbc:postgresql://leftover:5432/orders <- OriginAwareSystemEnvironmentPropertySource {name='systemEnvironment'}
    2. jdbc:postgresql://prod-db:5432/orders <- 'file application-prod.yaml' via location 'optional:classpath:/''}
    3. jdbc:h2:mem:default                <- 'file application.yaml' via location 'optional:classpath:/''}
  holders that lost: 2

The profile-specific file is still loaded and still holds its value -- it is listed,
and it lost. Config data is item 3 in the documented precedence list; OS environment
variables are item 5, and later items win.

== the full property-source stack, in order ==
$ curl -s localhost:8080/sources
   1. MapPropertySource                  server.ports
   2. ConfigurationPropertySourcesPropertySource configurationProperties
   3. SimpleCommandLinePropertySource    commandLineArgs
   4. StubPropertySource                 servletConfigInitParams
   5. ServletContextPropertySource       servletContextInitParams
   6. PropertiesPropertySource           systemProperties
   7. OriginAwareSystemEnvironmentPropertySource systemEnvironment
   8. RandomValuePropertySource          random
   9. OriginTrackedMapPropertySource     Config resource 'class path resource [application-prod-metrics.yaml]' via location 'optional:classpath:/'
  10. OriginTrackedMapPropertySource     Config resource 'class path resource [application-prod-db.yaml]' via location 'optional:classpath:/'
  11. OriginTrackedMapPropertySource     Config resource 'class path resource [application-prod.yaml]' via location 'optional:classpath:/'
  12. OriginTrackedMapPropertySource     Config resource 'class path resource [application.yaml]' via location 'optional:classpath:/'
  13. ApplicationInfoPropertySource      applicationInfo