drive: hide dangerous config from the configurator
drive: hide dangerous config from the configurator

This hides:

- "use_created_date"
- "use_shared_date"
- "size_as_quota"

from the configurator (rclone config) as they interfere with normal
operations and shouldn't be set in a backend config.

They can still be put in the config file by hand and will still work
as variables, etc.

This adds some more docs to "size_as_quota" also.

Fixes #3912

ncw/rclone,ncw/rclone,ncw/rclone,ncw/rclone