Flip --experimental_worker_allow_json_protocol (bazelbuild#14749)

Based on the discussion here
bazelbuild#13607 we want to flip this and
leave it around temporarily, but there are also some refactorings coming
around how to do that. This flips the value now so it can be used
without the flag sooner in rolling releases.

Closes bazelbuild#13745.

PiperOrigin-RevId: 423831532
(cherry picked from commit 9e16a64)

Co-authored-by: Keith Smiley <keithbsmiley@gmail.com>

src/main/java/com/google/devtools/build/lib/worker/WorkerOptions.java

@@ -48,7 +48,7 @@ public class WorkerOptions extends OptionsBase {
 
   @Option(
       name = "experimental_worker_allow_json_protocol",
-      defaultValue = "false",
+      defaultValue = "true",
       documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
       effectTags = {OptionEffectTag.BUILD_FILE_SEMANTICS},
       help =