Add extra logging to keyshare and cron-jobs

[DibranMulder]

At the moment, there is very little logging available from the keyshare server.
Also, it is impossible to see if the keyshare-cronjob is building up a 'queue' of emails which need to be sent, or that is doing fine.

[dobby-coder]

/dobby fix — add structured logging to the keyshare server and the email cron-job: log request/session activity in the keyshare server, and have the cron-job log the size of the pending-email queue and per-run send counts so queue build-up is observable, as described above.