Support resource quotas for namespaces

[minrk]

It would probably be useful to support ResourceQuotas for user namespaces.

I think the simplest version of this is to add a resource_quota_file setting for a path to a regular ResourceQuota yaml spec, and apply it to all kbatch namespaces. kbatch doesn't need to understand the quotas, just how to create them.

Someday, per-user quotas may make sense via templating or something, but I think that can wait.