Ability to filter out archived Bitbucket Server repositories

Created by: slimsag

Bitbucket Server doesn't have a way to archive repositories natively, so it relies solely on social constructs to denote repositories as archived currently (e.g., saying "don't use this" in the README).

This also means in Sourcegraph there is no way to filter out archived repositories using the archive: search filter -- because Bitbucket can't tell us which repositories are archived.

I propose we detect Bitbucket Server archived repositories by looking for the label on repositories named archived (this is non-standard, but is one obvious way to support this):

Requested by a user at https://app.hubspot.com/contacts/2762526/company/407948923