Turn the "closed" property on cluster repositories into a nice boolean
Summary:
Ref T10883. Ref T13120. There's an existing "closed" property on repository services that stops new repositories from being allocated there.
Turn it into a nice boolean.
Test Plan: Toggled the value on/off using a nice <select /> with helpful labels instead of a text area.
Reviewers: amckinley
Reviewed By: amckinley
Maniphest Tasks: T13120, T10883
Differential Revision: https://secure.phabricator.com/D19355