Generate [repository index files](https://wiki.debian.org/DebianRepository/Format) for `debian:suite` collections. This is the first step in adding repository hosting to Debusine. From our [planning document](https://docs.google.com/document/d/12CvqlRa_vBjjaQItizwsHww-6HXx9-QPU2cpqxnfjvs): MUST: Generate indexes for a repository - Define the artifact categories used to store repository indexes - Define relations between index artifacts, if any - Define how overrides are stored and provided - Enable debian:suite collection to store such artifacts as well as packages - Implement the logic to actually generate the indexes - Likely as a server task processing a collection into a set of artifacts - Integrate overrides and repository metadata - Implement in an extendable way so that it’s easy to later add [AppStream](https://wiki.debian.org/AppStream) metadata, Translations, or other possible repository metadata - Scheduling (triggered, cron, …) - Contents, Packages, Release might need to be separate tasks in a workflow; Release could be generated in a lock-free way by considering the state of the suite at a given timestamp