Output build graph using quarkus.builder.graph-output property

Add `BuilderConfig` to eliminate build warnings

core/builder/src/main/java/io/quarkus/builder/BuildChainBuilder.java

@@ -30,7 +30,7 @@
  */
 public final class BuildChainBuilder {
 
-    private static final String GRAPH_OUTPUT = System.getProperty("jboss.builder.graph-output");
+    private static final String GRAPH_OUTPUT = System.getProperty("quarkus.builder.graph-output");
     static final boolean LOG_CONFLICT_CAUSING = Boolean.getBoolean("quarkus.builder.log-conflict-cause");
 
     private final BuildStepBuilder finalStep;

core/runtime/src/main/java/io/quarkus/runtime/BuilderConfig.java

@@ -0,0 +1,29 @@
+package io.quarkus.runtime;
+
+import java.util.Optional;
+
+import io.quarkus.runtime.annotations.ConfigItem;
+import io.quarkus.runtime.annotations.ConfigPhase;
+import io.quarkus.runtime.annotations.ConfigRoot;
+
+/**
+ * This configuration class is here to avoid warnings when using {@code -Dquarkus.builder.=...}.
+ *
+ * @see io.quarkus.builder.BuildChainBuilder
+ */
+@ConfigRoot(name = "builder", phase = ConfigPhase.RUN_TIME)
+public class BuilderConfig {
+
+    /**
+     * The path to the graph output file.
+     */
+    @ConfigItem
+    public Optional<String> graphOutput;
+
+    /**
+     * Whether or not to log the cause of a conflict.
+     */
+    @ConfigItem
+    public Optional<Boolean> logConflictCause;
+
+}