Discovery setting can't set in a different profile when use Discovery First Lookup.

Describe the bug
When I set discovery setting in specific profile(e.g. application-test.yml), it will raise an exception.

java.lang.NullPointerException: null
	at org.springframework.cloud.config.client.ConfigServerInstanceProvider.getConfigServerInstances(ConfigServerInstanceProvider.java:57) ~[spring-cloud-config-client-3.1.0-RC1.jar:3.1.0-RC1]
	at org.springframework.cloud.config.client.ConfigServerInstanceMonitor.refresh(ConfigServerInstanceMonitor.java:90) ~[spring-cloud-config-client-3.1.0-RC1.jar:3.1.0-RC1]

The bootstrapContext register Binder with activationContext after contributors process imports.
So in ConfigServerConfigDataLocationResolver#resolveProfileSpecific method, the bootstrapContext has no activationContext, and the resolverContext has activationContext.
Therefore, resolverContext resolved spring.cloud.config.discovery.enabled is true, However
bootstrapContext resolved result is false. It cause the ConfigServerInstanceProvider.Function register in EurekaConfigServerBootstrapper is null.

Sample
The configuration in application-test.yml

eureka:
  client:
    serviceUrl:
      defaultZone: http://127.0.0.1:8761/eureka/
spring:
  config:
    import: 'optional:configserver:'
  cloud:
    config:
      enabled: true
      discovery:
        enabled: true
        serviceId: configserver

Start at ConfigServerConfigDataLocationResolver#resolveProfileSpecific and compare the resolverContext and bootstrapContext activation contexts described in the report. Trace ConfigServerInstanceProvider#getConfigServerInstances, ConfigServerInstanceMonitor#refresh, and EurekaConfigServerBootstrapper. Done means the application-test.yml discovery settings no longer cause a NullPointerException and the discovery provider is available.