Convert executeKart to a QgsTask

[pfw]

Is your feature request related to a problem? Please describe.
executeKart currently uses subprocess.Popen directly and doesn't run in seperate threads. This has a couple of issues around the UI locking up on long operations and difficulty in correctly reporting progress without causing other race conditions.

Describe the solution you'd like
Move executeKart from using subprocess.Popen directly to using that within a QgsTask

[pfw]

Docs for how to implement a QqsTask https://docs.qgis.org/3.22/en/docs/pyqgis_developer_cookbook/tasks.html

executeKart is often called as one of many steps in a process and so we need a way for code to call a task, wait for the response, call another task etc. Or any block of code that calls kart should itself be entirely within a QgsTask so that the UI doesn't block waiting for a response.