chore: release gapic-generator-java v0.0.21 with gapic_metadata.json support

Committer: @miraleung
PiperOrigin-RevId: 358516065

Author: Google APIs

WORKSPACE

@@ -174,7 +174,7 @@ apple_support_dependencies()
 # Java
 ##############################################################################
 # Java microgenerator.
-_gapic_generator_java_version = "0.0.20"
+_gapic_generator_java_version = "0.0.21"
 
 http_archive(
     name = "gapic_generator_java",