Added Authentication

Related issues

Acceptance criteria

• Implemented code changes don't diverge from the related issue.
• Documentation reflects the status quo after merge.
• Version number is incremented according to SemVer. (Snapshot versions are not merged/released.)
• Only released versions of dependencies are used (i.e. no snapshot versions).
• Pipeline still works.
• GitLab issue is up-to-date.

If necessary, the following sections have been updated:

• Swagger
• Readme.md
• Documentation

Proposed squash commit message

Added OAuth Authentication to Application

* Controller Methods annotated with @PreAuthorize
* Every Controller Method checks if a valid jwt token is present
* Added AuthorizationService to get the AuthenticatedUser in Controllers. This Object can later be passed to Domain Methods, to check permissions

Closes #36 (closed)