Fix postgresql isolation level

[30350n]

So after fixing my deployment again, I was getting a whole bunch of django.db.utils.OperationalError: could not serialize access due to concurrent update errors which also made the interface feel noticeably sluggish (things would straight up not load ~50% of the time).

Looking at the existing issues regarding that error, this seems to be caused by the postgresql isolation level setting being set to ISOLATION_LEVEL_SERIALIZABLE, which seems to have been messed up during the switch to Django 4 in #6173.

I tested this patch on my production server and by clicking through random pages furiously for 2 minutes and didn't get any further errors (before there were sometimes multiple when visiting a single page).

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[SchrodingersGat]

@30350n thanks for giving attention to this :)

[SchrodingersGat]

@30350n ok, something has broken here...

https://github.com/inventree/InvenTree/actions/runs/8041284048/job/21960366000

[SchrodingersGat]

Ok, we recently moved away from psycopg2 module. It is now psycopg that needs to be imported. Not sure how the initial tests passed here

[30350n]

Hmm, I checked and it wasn't part of the dependencies before #6173 either.

[30350n]

And the deployment docs mention that you should install it, so I figured that'd be the way to go.

[30350n]

Also seems like Django 4 requires psycopg2.

[matmair]

@30350n they call out that they are switching away in the release notes https://docs.djangoproject.com/en/5.0/releases/4.2/#what-s-new-in-django-4-2 so depending on v2 instead of v3 will probably be a problem in the future

[matmair]

we are on 4.2 so these are the supported/recommended engines https://docs.djangoproject.com/en/4.2/ref/databases/#postgresql-notes

[30350n]

Ah yeah, I was looking at the docs for 4.0 I see, my bad. I'll make another PR to switch to psycopg that also fixes the docs.

[SchrodingersGat]

Thanks for addressing this so speedily :)

[30350n]

No Problem ^^