Allow users to view their user_id

Please let the site's users view their user id, so that they will then be able to ask 3rd-party sites & services to fetch their MetaCPAN favorites or interact in other ways.

One such service is https://www.perlmodules.net/, where retrieving one's own list of favorites would be quite useful.

So, exposing the user id under https://metacpan.org/account/profile might be the most appropriate place.
