Commit contains all backend tasks for the seventh sprint.

The focus of sprint 6 was to:

- create statements from mails
- upload statement responses
- send notification mails to users on important task traversals
- add the department contributions functionality
- send statement response mail to the customer

Details:

[TOB-360] fix: mail backend and pdf generation

* fixed minor issues in pdf generation if textblock is too large to ever
  printed on a single page. This will return a 400 response now.
* added mail notification in case of negative approval result to inform
  the spa-oic about the negative approval.
* fixed potential 500 when uploading an attachment with tagIds and the
  database updates were not committed fast enough.

[TOB-355] feat: transfer mail text and attachments

* added interface to transfer mail text as statement attachment
* added interface to transfer mail attachments as statement attachments
* added sourcemailId parameter to statement database table and models
* added removed demo ServiceTask worker and servicetask handling because
  it is not used in the project context
* added testcases to verify the new transfer mail interfaces

[TOB-321] fix: text rendering in pdf

* fixed skip of the last word of line in cases of line wrappings
* added additional space between textblocks when no newline

[TOB-83] feat: internal mail notification

* added interface to sync users from keycloak to add notification
  receivers to the database
* added MailConfiguration to parse mail configuration json that contains
  the message texts for statement response and notification messages
* added viewRepository to get contributing division members
* enhanced NotfiyService to create notification mails on specific
  notification scenarios.
* enhanced TaskAdditionsService to derrive notification scenarios from
  workflow task transitions
* fixed a minor bug in the Lexer to support single underscores in
  textblocks. Enhanced testcases for validation.
* updated backend REST interface specification and database schema

[TOB-343] feat: replace statement response

* when uploading a statement response, already existing attachments with
  tag "statement" are removed before the new attachment is stored.

[TOB-333] contributions interface

* added interface to get statement workflow department contributions
* added interface to set statement workflow department contributions
* added interface to set user department contribution for statement
  workflow

[TOB-322,323,324] feat: statement response mail

* updated api definition
* added REST interface to send statement response mail
* added TaskAdditionsService to send statement response mail after
  successful response approval
* added Template for response mail data
* update statement workflow model according to the response mail logic
  (required variables, manual response, reconfigure statement)

Signed-off-by: Tobias Stummer <stummer@develop-group.de>