Make the repository "Filesize Limit" and "Clone/Fetch Timeout" configurable in the UI

Summary: Depends on D19830. Ref T13216. See PHI908. See PHI750. See PHI885. Allow users to configure a filesize limit, and allow them to adjust the clone/fetch timeout.

Test Plan:
{F6021356}

• Configured a filesize limit and pushed, hit it. Made the limit larger and pushed, change went through.

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: yelirekim, PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13216

Differential Revision: https://secure.phabricator.com/D19831