* open up API for plugins by removing internal
* use constants in entity column definition
* simplified entity management API
* bump packages
* allow installing assets and run database migrations independently
* bump to apidoc-bundle 5
* do not duplicate http method in API operationId
* new security entries in Open API definition
* changed API UI provider for Swagger to Stoplight, improved endpoint titles, hide internal endpoints
* deactivate swagger json endpoint
* added serializer attributes for API usage
* new setters to fill invoice data from fixture
* re-usable fixture helper methods
* added API endpoints to fetch invoices
* adjust tests
