Upload GN CIPD package

This change always builds the CIPD package for GN for CI builds and
when requested also uploads that package to CIPD server.

Change-Id: Idc62ed9c6b4c491426b2c7e26b87cad03a206d5e
Reviewed-on: https://gn-review.googlesource.com/1781
Reviewed-by: Andrii Shyshkalov <tandrii@google.com>
Reviewed-by: Vadim Shtayura <vadimsh@chromium.org>
Reviewed-by: Scott Graham <scottmg@chromium.org>
Commit-Queue: Petr Hosek <phosek@google.com>