Add relative file paths to config_to_policy.rs

[j-lanson]

We want the policy files generated by config_to_policy.rs to have file paths relative to the Hipcheck.toml file that created them, similar to what #rel() accomplishes in policy file parsing. This will require recording and passing along to location of Hipcheck.toml to the config_to_policy.rs entrypoint, which is not currently immediately accessible.

At the end of this, config fields like binary-path should take "Binary.kdl" as a path and combine it with the parent dir of the source "Hipcheck.toml" file.