This eliminates the oddness of having multiple discovery client beans and related behavior and simplifies bootstrap significantly.
Moves to ConfigServerInstanceProvider.Function for config client bootstrap.
Removes conditions for dealing with DiscoverClient in parent context.
Updates tests to reflect the new reality of no DiscoveryClient in bootstrap.
Renames config bootstrap to EurekaConfigServerBootstrapConfiguration
Fixes gh-3795
See https://github.com/spring-cloud/spring-cloud-gateway/issues/1514