Issue description

We are refactoring the dashboard manager api, to remove the dependency on MySQL. Previously, some managed fields were saved in mysql. After refactoring, we moved these fields to ETCD. I think APISIX's json schema should also support this part of the fields to avoid data being filtered out.

Here is the detail:

create_time and update_time for route,upstream,service,consumer,ssl
validity_start and validity_end for ssl

this four fields are all int type for Unix timestamp.