Add ability to define default attributes of new tasks

Hi, having a config to specify default attributes (e. g. `project:inbox`) for newly created tasks would be helpful.
For example a person using `project:inbox` could want to add all new tasks to a project called "inbox" used for separating unrefined items from reviewed & refined items (this is an example).

My personal use case would be to auto-destroy tasks older than two months. I try to avoid tasks becoming stale. My shell alias for creating tasks always adds `until:2month` which I found to be quite helpful. This breaks when I use some other means of creating new items, e. g. `task add` executing task via some other alias.

Having the ability to add default attributes as well as being able to override these defaults by specifying something else (e. g. `task add pro:kitchen foo` won't go to `inbox` and `task add until: bar` will never expire).

Thanks!