Bump gRPC to 0.6.0

Author: dsyer

start-site/src/main/resources/application.yml

@@ -130,7 +130,7 @@ initializr:
         versionProperty: spring-grpc.version
         mappings:
           - compatibilityRange: "[3.4.0,3.6.0-M1)"
-            version: 0.5.0
+            version: 0.6.0
       spring-modulith:
         groupId: org.springframework.modulith
         artifactId: spring-modulith-bom