git: Hide refs for upload-pack

Currently we are relying on an omnibus setting that sets a git config value to hide certain hidden refs during transfer. However, we no longer want to rely on git config files that are external to Gitaly but rather inject config values we need directly into the command.

We already do this for receive-pack but not for upload-pack. Add the corresponding config for upload-pack.

Changelog: changed

fixes: #4358 (closed)