applied default value in case legacy config is used (#787)

(cherry picked from commit 1e85d70)

spring-boot-starter-camunda/src/main/java/io/camunda/zeebe/spring/client/configuration/ZeebeClientConfiguration.java

@@ -382,7 +382,12 @@ public boolean useDefaultRetryPolicy() {
 
   @Override
   public boolean preferRestOverGrpc() {
-    return camundaClientProperties.getZeebe().isPreferRestOverGrpc();
+    return getOrLegacyOrDefault(
+        "preferRestOverGrpc",
+        () -> camundaClientProperties.getZeebe().isPreferRestOverGrpc(),
+        () -> null,
+        DEFAULT.preferRestOverGrpc(),
+        configCache);
   }
 
   @Override