superproject: Log argv parameter of syncstate as 'data-json'.

Fixed: "we need to make a special case for logging the argv; it
should probably be a "data-json" event so that we log this directly as
an array rather than an encoded string.

Tested:
$ repo_dev sync

Verified event logged for argv is "data-json".

$./run_tests

Bug: [google internal] b/201102002
Change-Id: I18ccec79c73c8dc931cb8afc472b2361db8aea4c
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/319055


Reviewed-by: Josh Steadmon <steadmon@google.com>
Reviewed-by: Xin Li <delphij@google.com>
Tested-by: Raman Tenneti <rtenneti@google.com>