NXDRIVE-2276: [Direct Transfer] Introduce the notion of sessions

[rom1win]

When doing a Direct Transfer, the files/folders should to be
tight to a session.
A new migration has been added to handle the Sessions.

A test for the migration has been added.

An old_functionnal test has been added to check the session
creation/update system.

[nuxeojenkins]

View issue in JIRA: NXDRIVE-2276: [Direct Transfer] Introduce the notion of sessions

[BoboTiG]

It seems good 👍

[sourcery-ai]

Sourcery Code Quality Report (beta)

❌  Merging this PR will decrease code quality in the affected files by 0.01 out of 10.

Quality metrics	Before	After	Change
Complexity	2.67	2.65	-0.02 🔵
Method Length	62.22	62.65	0.43 🔴
Quality	8.48	8.47	-0.01 🔴

Other metrics	Before	After	Change
Lines	6486	6658	172

Changed files	Quality Before	Quality After	Quality Change
nxdrive/objects.py	8.09	8.07	-0.02 🔴
nxdrive/engine/engine.py	8.47	8.47	0.00
nxdrive/engine/processor.py	7.23	7.23	0.00
nxdrive/engine/dao/sqlite.py	8.80	8.80	0.00
tests/old_functional/test_direct_transfer.py	8.71	8.66	-0.05 🔴
tests/unit/test_engine_dao.py	8.23	8.22	-0.01 🔴

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Overall	Recommendation
nxdrive/engine/processor.py	Processor._execute	134	1036.03	0.05	Reduce complexity. Split out functionality
nxdrive/engine/processor.py	Processor._synchronize_locally_created	98	887.25	0.20	Reduce complexity. Split out functionality
nxdrive/engine/dao/sqlite.py	EngineDAO._migrate_db	31	521.83	2.30	Split out functionality
nxdrive/engine/processor.py	Processor._synchronize_remotely_modified	33	322.78	2.49	Split out functionality
nxdrive/engine/processor.py	Processor._synchronize_remotely_created	27	282.81	3.09	Split out functionality

Please see our documentation here for details on how these metrics are calculated.

We are actively working on this report - lots more documentation and extra metrics to come!

Let us know what you think of it by mentioning @sourcery-ai in a comment.