Feature: disable polling for apps with same repo url

[vishal-dt]

Description

Currently, each time an app is created a new repo is checked out in git sensor. Each time the watcher polls changes from upstream it does it for each and every repo. In scenarios where multiple applications have same git repo url this leads to resource wastage and slow polling rate.

Proposal

Disable polling for repos with same url by referencing to one single repo for git related information.