Fix validate config

[surge119]

Summary

The initial implementation would fail for overrides, since the path provided into parse_rule is the override path, instead of the path to the config file, which is expected.

Test Plan

Included

[amyreese]

I'd prefer to use the root terminology instead of parse_path. Also, is there ever a case where root here wouldn't always be path.parent? Can we avoid the extra argument to validate_config and validate_rules, and just set root = path.parent at the top of the function?

Edit: in merge_configs, we just always pass path.parent straight through to parse_rule, and I think that's the correct behavior.

[surge119]

Also, is there ever a case where root here wouldn't always be path.parent? Can we avoid the extra argument to validate_config and validate_rules, and just set root = path.parent at the top of the function?

Only because of testing. Since the tests use a temporary directory, using parent for them would cause them to fail. But I suppose the tests can create new rules to reference