FTP provider: Maintain threads

[iLLiCiTiT]

Is there an existing issue for this?

• I have searched the existing issues and added correct labels.

Description

Current Behavior

FTP provider is spawning new python threads but is not handling their joining, that can lead to dangling processes.

Expected Behavior

Threads of the provider should be joined correctly, and if it is possible it should also stop them if force closing is requested.