Introduce environments dev, test, prod

* If nothing specified the dev environment is used as default.
  The dev environment uses a in-memory database and creates
  test data, but uses a mocked mail sender.

* The test environment uses a mysql database, creates no
  test data and used a mocked mail sender too.

* The prod environment is equals to test environment, but uses
  the spring java mail sender to be able to send emails.

* refs #17551
Make properties for mail recipients (boss, office etc.) obsolete

* The correct mail recipients are now fetched by person service
  by their role. No need anymore to define mail recipients in
  `mail.properties` - except the technical manager of the
  application.

* refs #17551
Add logging after sent email.

* refs #17551
Adjust mail recipients for cancelation of applications for leave

* Only office members get now an email notification if a person
  cancels his already allowed application for leave.

* refs #17551