Set sensible defaults for core.packedGitLimit and core.packedGitWindowSize

There are currently two knobs to tune memory usage in git-pack-objects(1). core.packedGitWindowSize and core.packedGitLimit.

git-pack-objects(1) can consume large amounts of memory during clones when packing objects into packfiles. It would be helpful to decide and codify some sensible default values for this configuration to reduce the danger of K8s OOM pod lifecycle events.