Support sharing lists with other users

There's already a web service for this: http://iodocs.apps.intermine.org/humanmine/docs#/ws-list-shares/POST/lists/shares

We're not sure how widely used this feature was in the legacy webapp.

Start with the POST /lists/shares endpoint in the linked I/O Docs service and inspect how list operations are represented in this repository. The issue does not name files, tests, or acceptance criteria; clarify whether legacy behavior matters and define the supported sharing flow before implementation. Done should mean the agreed sharing behavior works against the service and is covered by suitable checks.

Written by the indexing model from the issue text.