util.tlsref: New util library to encapsulate the Mozilla/TLSRef recommendations Previously we embedded this data directly into core.certmanager. This splits it out, for various benefits: - Removes data from the business logic (the config parsing is complex enough as it is) - Allows easier testing and tracking of the data (this commit adds various consistency checks, so that we can have more confidence in future updates to the data not breaking stuff) This library also supports multiple versions of the recommendations. Previously we picked a single version, and put that into certmanager. But this meant we had to make choices for our users, and one of the choices is between advancing security standards and ensuring we don't break connectivity for people doing minor upgrades (deterring people from performing minor upgrades would have a security impact too). This library supports the concept of a "default" and a "latest" version, so we are now free to add new versions into stable releases, and admins can pick between compatibility and security.