Implement unencrypted log capture without attachments

Summary:
This differential implements API that enables to monitor and capture backup logs. At this point logs are unencrypted, without attachments. Future differentials will improve those deficiencies. This diff doesn't break the app since log capture is not actually called yet.

How does log capture work?

1. We attach session to database connection and session starts to accumulate logs.
2. Each time we call captureLogs we read logID from metadata table in database, store log to file identified by this logID and finally write incremented logID to the database.

Test Plan:

1. Add a call to DatabaseManager::getQueryExecutor().captureBackupLogs() just before DatabaseManager::getQueryExecutor().commitTransaction() in BaseDataStore.h.
2. Use the app: make drafts, send messages, update threads colours etc..
3. Periodically download app container from XCode.
4. Ensure that there are created backup-0-log-xxx files that contain unreadable bytes mixed with readable strings with database table names and database entities fields values.

Reviewers: michal, kamil

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10835