Redo wrap_exception and add one for the Django Connector

[ewjoachim]

Closes #981

Django connector was missing an exception mapper transforming Psycopg (2 or 3) exceptions to procrastinate exception, especially the queueing lock exception that we handle gracefully.

In order to make a proper implementation, I redid wrap_exceptions everywhere using contextlib.contextmanager.

Successful PR Checklist:

• Tests
  • (not applicable?)
• Documentation
  • (not applicable?)

PR label(s):

• PR type: breaking 💥 Contains breaking changes
• PR type: feature ⭐️ Contains new features
• PR type: bugfix 🕵️ Contains bug fix
• PR type: miscellaneous 👾 Contains misc changes
• PR type: dependencies 🤖 Contains only dependencies updates
• PR type: documentation 📚 Contains documentation updates

[github-actions]

Coverage report

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
procrastinate
psycopg_connector.py
sync_psycopg_connector.py
utils.py
procrastinate/contrib/aiopg
aiopg_connector.py
procrastinate/contrib/django
django_connector.py
procrastinate/contrib/psycopg2
psycopg2_connector.py
procrastinate/contrib/sqlalchemy
psycopg2_connector.py
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