Make repository display name configurable via configuration file

Created by: tazjin

Feature request description

Currently the display name of repositories in configuration files is determined based on their array index in the configuration. It should be possible to override this to an arbitrary string via the configuration.

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

We are trying to migrate to configuration-as-files, but are running into being unable to set the display name which blocks us from using this (as it affects URLs).

Note that there is also code that determines which diffs to apply based on this display name. If I'm reading this correctly it means that configuration can get out of sync if reordered in the configuration file. Actually this part should be fine, since it checks the serialised config also.