New & improved API endpoints

[lambdaschmied2]

Instead of adding more issues to the back-end repo right now, I think it is a good idea to document here which endpoints could benefit from some improvements to make the front-end better. When we approach a stable release we can take care of it as a whole.

@antonAtGit

[lambdaschmied2]

Extend endpoint tasks
Add option to get the process definition name for each task with one request

[lambdaschmied2]

Extend enpoint process-definition/statistics
Add option to only get the statistics for a single process definition &process-defininition-id=xxx
(https://docs.camunda.org/rest/camunda-bpm-platform/7.22/#tag/Process-Definition/operation/getProcessDefinitionStatistics)