Add configuration to poll for newly created repos

Created by: christinelovett

Feature request description

The code host update heuristics can lead to long delays (up to 8hrs) for newly created repositories to be picked up by Sourcegraph. Admins would like the ability to configure a predictable interval of polling for new repos.

Is your feature request related to a problem? If so, please describe.

Users are confused and unclear on when a new repo will make it into Sourcegraph.

Requested by: https://app.hubspot.com/contacts/2762526/company/6286373436?globalSearchQuery=ge