Commit contains all backend tasks for the project ramp-up phase.

[TOB-97] chor: Add initial backend project setup.

[TOB-106] feat: basic session and version REST-IF.

- added /userinfo interface that provides user details and roles
- added /keepalive-session interface that extends jwt validity
- added /versioninfo interface that provides service name and version
- added /logout interface to invalidate the jwt token

[TOB-106] feat: basic session and version REST-IF.

- added openapi.yaml containing basic interface definition
- cleaned up response types of the basic interface implementation to match the definition

[TOB-106] feat: basic session and version REST-IF.

- added deploy folder containing a keycloak test user setup script
- added role guards for /logout, /userinfo, /version and  /logout interfaces

[TOB112, TOB113, TOB114] feat: Dashboard Backend.

- added jpa database models for TblStatement, TblContact and
  TblAttachment
- added TblStatementRepository to access the TblStatement database
- added StatementService as a central service to access and manipulate
  Statements
- added StatementController for providing REST interfaces to access and
  manipulate Statements
- added StatementOverviewService as a central service to list and search
  statements
- added StatementOverviewController for providing REST interfaces to
  list and search statements
- Removed Requirement for valid Token to access the /version REST
  interface
- added Tests to verify the already implemented REST interfaces of the
  StatementController and the StatementOverviewController
- Added database parameters to the application.yml

[TOB119, TOB120] feat: Neue Stellungnahmen Backend

- added View models of Statment and Attachment
- added Controller classes that provide REST interfaces to create read
  statements and attachments
- added utility to convert common datatypes to and from string
  representation. (e.g. LocalDate)
- added StatementService to access and manage statements and therir
  attachments.
- added JPA Entities for attachment, statement and contacts

- added Tests to verify the new statment and attachment rest interfaces
- added Tests to verify the StatmentService

- minor cleanup, code and comments

- added sql helper to create the initial database tables

[TOB 112] fix: Set statement title value on GET

- StatementDetailModel title was not set correctly.

[TOB-124] feat: Added external libs to NOTICE.md

- added references to external libraries to NOTICE.md
- cleaned up the legal headers of own code, where EPL 2.0 was missing

[TOB-121, TOB-122, TOB-124] SW-Architecture

- Added initial architecture documentation based on the arc42 template
- documentation currently contains a list of used ok-modules, used third
  party libraries and their licences
- documentation contains a container diagram for the Statment Public
  Affairs module to show the communication between the main internal
components and the external modules.

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