Hydra: Enable debuginfo indexing for all store paths

[edolstra]

Is your feature request related to a problem? Please describe.

Currently, we only maintain the DWARF debuginfo index (https://cache.nixos.org/debuginfo) for store paths that are part of NixOS/Nixpkgs releases. This means that dwarffs cannot find debug symbols for other store paths, in particular for Nix releases built by Hydra. This makes it harder to debug core dumps from Nix crashes in the field.

Describe the solution you'd like

Enable the index-debug-info option on store_uri in hydra.conf.

This should allow us to get rid of index-debuginfo.cc in the channel updater scripts.

Describe alternatives you've considered

Additional context