- Introduce new Usecase
  - annotation `UseCaseAdminUpdatesUserEmailAddress`
  - usecase identifier `UC_ADMIN_UPDATES_USER_EMAIL_ADDRESS`
  - documentation via asciidoc + annotation data
- Introduce new event/domain message
  - MessageID
  - MessageDataKey
  - enhanced UserMessage, contains now former email address (optional)
- Implemented Logic
  - introducing new service `UserEmailAddressUpdateService`
  - Role allowed: only admin
  - added unit tests for service
- Add REST access
 - introduced new method inside UserAdministrationRestController
 - Role allowed: only admin

- additional (but not related)
  - introducing TestCanaryException, so easier to check
    exception handling

- Test API changes
  - added new method inside TestURLbuilder for new rest call
  - added new test call method inside class `AsUser`
    to make it callable inside integration test
- Integration test
  - wrote test which does change as an administrator an existing
    user.
  - checks if user email address has been changed
  - checks if an email was sent to new user email address
  - checks if an email was sent to old user email address

Additional (because necessary):
- TestAPI changes
  - added test user detail information to fetch old email address
    from user for testing
  - changed AssertEmail and introduced TextSearchmode

- introduced `UserEmailAddressChangedNotificationService`
- added tests to check mail content and subjects are correct
  created

- changed integration test
  - email subject text a little bit different

Additional
- same smaller changes at update service
- MockEmailAccess improved error output, contains now text search
  mode info

- applied source formatting by spotless
- fixed failing unit test
- added missing SPDX header related to #633

- added simple DAUI action to change email address for user
- added missing method in `DeveloperAdministration` class
- added new action inside `CommandUI`

- fixed typo in emum