Feature Request: Minimum entries before selection

I would like to see the ability to set a minimum # or % of users who enter a give-away before the event can fire and select a random person. For example, I could set it for 2 weeks and >10%. Or perhaps 2 weeks and >20. If I type % in the command, it calculates the current members of that channel or server and sets it to that number. Then it must wait 2 weeks, and if less than that number has entered, it waits till that number has been reached or cancels the giveaway.

The issue names no files, tests, or entry points. Start by locating the existing giveaway command and selection flow, then determine how a configurable minimum count or percentage and waiting period should interact; done means the giveaway waits, selects, or cancels according to the configured threshold.

Written by the indexing model from the issue text.