[native] refactor CommCoreModule to allow cancellable tasks

Summary:
context: ENG-2139

refactor CommCoreModule methods that schedule tasks on the database thread to allow them to be canceled - all methods except clearSensitiveData that should not be canceled - is responsible for canceling others.

Test Plan:

1. Build app for both iOS and Android
2. Check if previous integrations with the database work properly eg. by adding some drafts etc.
3. Make sure that there is no operation executed on database thread or added to queue when sensitiveDataCleaner is called

Reviewers: marcin, jon, tomek, atul

Reviewed By: marcin, tomek

Subscribers: ashoat, tomek, atul, abosh

Differential Revision: https://phab.comm.dev/D5579