Write a protocol for L4 reviewer/publishers

[sebbacon]

This is TBC and will require lots of discussion. @amirmehrkar is currently researching best practice in other TREs.

At a minimum this should be a checklist + guidance. Longer term it could perhaps be supported by tooling (online workflow/forms, scripts for verifying things, etc)

Lots of useful discussion in https://github.com/opensafely/cohort-extractor/issues/71