Adding logging related to CORS configuration

Removing unused `allow_placeholder_references` property that causes confusion with `auto_create_placeholder_references`
Improving `.dockerignore` so that it ignores specific target files/directories that are generated by MVN/java, but not the .war file (so that compiled .war files can be easily turned into a docker image)

src/main/java/ca/uhn/fhir/jpa/starter/BaseJpaRestfulServer.java

@@ -48,6 +48,7 @@ import java.util.*;
 import java.util.stream.Collectors;
 
 public class BaseJpaRestfulServer extends RestfulServer {
+  private static final org.slf4j.Logger ourLog = org.slf4j.LoggerFactory.getLogger(BaseJpaRestfulServer.class);
 
   @Autowired
   DaoRegistry daoRegistry;
@@ -270,6 +271,7 @@ public class BaseJpaRestfulServer extends RestfulServer {
     // showing a typical setup. You should customize this
     // to your specific needs
     if (appProperties.getCors() != null) {
+    	ourLog.info("CORS is enabled on this server");
       CorsConfiguration config = new CorsConfiguration();
       config.addAllowedHeader(HttpHeaders.ORIGIN);
       config.addAllowedHeader(HttpHeaders.ACCEPT);
@@ -279,9 +281,10 @@ public class BaseJpaRestfulServer extends RestfulServer {
       config.addAllowedHeader("x-fhir-starter");
       config.addAllowedHeader("X-Requested-With");
       config.addAllowedHeader("Prefer");
+
       List<String> allAllowedCORSOrigins = appProperties.getCors().getAllowed_origin();
       allAllowedCORSOrigins.forEach(config::addAllowedOriginPattern);
-
+      ourLog.info("CORS allows the following origins: " + String.join(", ", allAllowedCORSOrigins));
 
       config.addExposedHeader("Location");
       config.addExposedHeader("Content-Location");
@@ -292,7 +295,9 @@ public class BaseJpaRestfulServer extends RestfulServer {
       // Create the interceptor and register it
       CorsInterceptor interceptor = new CorsInterceptor(config);
       registerInterceptor(interceptor);
-    }
+    } else {
+    	ourLog.info("CORS is disabled on this server");
+	 }
 
     // If subscriptions are enabled, we want to register the interceptor that
     // will activate them and match results against them