Automatically generate bundles for bundle-uri

group::gitalygit has recently added bundle uri functionality to Gitaly. This feature allows git servers to advertise a http url to the git client for the git client to download a pre-baked bundle of the repository. This can be thought of as a repository cache. The main benefit is to the server. Instead of having to spin up git-pack-objects processes to pack up all the objects in a repository, this gets offloaded to an already generated bundle.

Currently, a cron job needs to be run to generate bundles for repositories. However, we'd like to make this configuration-less. Ideally, the feature could work this way:

1. In Project->Settings->Repository, an admin checks a checkbox labeled "Use Repository Bundle Caching" or something like that
2. On a git clone or git fetch, Rails can kick off a sidekiq job that will check if a bundle exists for a repository, and how old it is. If there is no bundle or if it's a very old bundle, then Rails can call Gitaly's GenerateBundleURI for that repository to generate a new bundle.
3. We can even add a sidekiq job to remove bundles for projects that have not been cloned/fetched from in a long time.

This issue is for discussing the design.

Updated 2024-06-03

Based on the discussions, we've decided to make bundle uris a transparent optimization to the GitLab rails application. This means that Gitaly will own the business logic for when and for which repositories to create a bundle URI.

1. Gitaly's config.toml will gain a config value for turning bundle uris on or off
2. Gitaly will decide based on heuristics whether or not to create a new bundle for a repository

Future will be tracked in gitaly#5803 (closed).