Add RestTemplateCustomizer to ConfigServicePropertySourceLocator

On the current project we use spring cloud config solution. The problem is that the config-server was deployed behind https load-balancer and we got the follfowing issues:

c.c.c.ConfigServicePropertySourceLocator : Could not locate PropertySource: I/O error on GET request for "****": java.security.cert.CertificateException: No subject alternative DNS name matching *** found.; nested exception is javax.net.ssl.SSLHandshakeException: java.security.cert.CertificateException: No subject alternative DNS name matching ***

According documentation we have solved that by custom ConfigServicePropertySourceLocator and RestTemplate configuration used there, but that was really tricky, we spend a few hours to find the proper client configuration.

The solution we'd like to have is just an opportunity to change RestTempalte config used in ConfigServicePropertySourceLocator via application.properties. In our case that could be something like spring.cloud.config.clinet.ssl.enalbed=false

Start at ConfigServicePropertySourceLocator and trace the RestTemplate configuration used for config-server requests. Check how application.properties can supply the requested client setting; done when that configuration can be changed without a custom locator or RestTemplate implementation.