Add optional setting to ignore an existing process on resuming a sync

[bjester]

Background

Morango stores the process ID on the sync session to prevent accidental resumption of a sync that is still active in another process. On Kolibri, if a sync was started via the UI but then fails, when a user tries to manually resume the sync outside of Kolibri's UI and task processing, the check that ensures the process ID is either the same or inactive can fail because the worker processing tasks is likely still a running and active process.

Summary

• Adds ignore_existing_process keyword arg to resume_sync_session allowing the bypass of checking the existing process ID

TODO

• Have tests been written for the new code?
• Has documentation been written/updated?
• New dependencies (if any) added to requirements file

Reviewer guidance

• The test and code review
• This work has been merged into this PR, which will run GH action checks against the updates

Issues addressed

Fixes #193

[jamalex]

Sorry for the delay! This looks great from my side -- I had one initial reaction wondering how this would actually be used via the CLI, then I remembered that part lives in Kolibri, so I'm assuming the option to tie into this will live there.