Default experimental_convenience_symlinks_bep_event to true

Seems like the only reason it never made it to true by default was oversight
or a lack of need. Seeing some reasons to default it true.

PiperOrigin-RevId: 633545914
Change-Id: I26e8a00968b0641b52c551cae70094f1891c6879

src/main/java/com/google/devtools/build/lib/buildtool/BuildRequestOptions.java

@@ -257,7 +257,7 @@ public class BuildRequestOptions extends OptionsBase {
 
   @Option(
       name = "experimental_convenience_symlinks_bep_event",
-      defaultValue = "false",
+      defaultValue = "true",
       documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
       effectTags = {OptionEffectTag.AFFECTS_OUTPUTS},
       help =