Add skuba.config.ts

[samchungy]

          This is great. I'd like to raise the `skuba.config.ts` proposal for review but that can be a separate PR 👍

Originally posted by @72636c in https://github.com/seek-oss/skuba/pull/1163#pullrequestreview-1419540213

[samchungy]

This is probably a better idea over overloading package.json. Additionally we can also provide some typing for the config