`config` verbs should use CWD if `-` is not provided

@kinelski requested exactly the edge case that I'd be ok with.

Currently, for `config` verb usage, one must provide `-a `. We should use the current directory and ascend looking for one if one isn't provided.

We don't want folks to accidentally `restore` or `push` or `reset` an assets.json that they don't intend, so this behavior will _only_ apply to the `config` verb.