Add org_jetbrains_kotlinx_kotlinx_serialization_json

This is needed by :androidx_datastore_datastore_core_okio_jvm_java to
unblock androidx autoroller.

DEPS file and build.gn files are not updated until after cipd has uploaded the package.

Change-Id: Iff255c6cad2fda625c3c495aaa414a4dd045cf02
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6936527
Commit-Queue: Benjamin Joyce (Ben) <bjoyce@google.com>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1513811}