scalar: enable path-walk during push via config

scalar: enable path-walk during push via config

Repositories registered with Scalar are expected to be client-only
repositories that are rather large. This means that they are more likely to
be good candidates for using the --path-walk option when running 'git
pack-objects', especially under the hood of 'git push'. Enable this config
in Scalar repositories.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>