Add Access Methods: ftps and/or sftp #410
Description
The current access methods https://ga4gh.github.io/data-repository-service-schemas/preview/develop/docs/#tag/AccessMethodModel do not include secure variants of ftp.
Our consortium is hoping to adopt DRS and one of our members noted that they have their files served over ftps. I propose adding ftps and maybe also sftp as access methods to the DRS standard.