Log details of uploaded manifests and blobs

This MR adds an info log message per (successfully) uploaded manifest and blob. Additionally, it adds a root_repo log key to all app log messages. This key is set to the root repository of a given request. For example, if uploading a blob to repositories foo/bar and abc, root_repo will be set to foo and abc, respectively.

These additional log messages and log key will help aggregate logs per GitLab group (such as how much blobs and manifests are being uploaded across all repositories of a given group, or how much space those are adding).