objstorage: Fix configuration toplevel key
objstorage: Fix configuration toplevel key

This also unifies the configuration amongst swh services.

Related D1178
Related T1533

SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site