Check for presence of Spring Boot autoconfig

Before using autoconfiguration utilities from Spring Boot we should
check they are on the classpath.

Fixes #367

Author: dsyer

spring-grpc-server-spring-boot-autoconfigure/src/main/java/org/springframework/boot/grpc/server/autoconfigure/security/OAuth2ClientAutoConfiguration.java

@@ -44,7 +44,7 @@
 @AutoConfiguration(
 		afterName = "org.springframework.boot.security.oauth2.client.autoconfigure.OAuth2ClientAutoConfiguration")
 @ConditionalOnSpringGrpc
-@ConditionalOnClass(InMemoryClientRegistrationRepository.class)
+@ConditionalOnClass({ OAuth2ClientProperties.class, InMemoryClientRegistrationRepository.class })
 @ConditionalOnOAuth2ClientRegistrationProperties
 @EnableConfigurationProperties(OAuth2ClientProperties.class)
 public final class OAuth2ClientAutoConfiguration {