Support multiple apps in testing initializer

[primal100]

Description

Allows the intializer to accept a mapping of app names to module list, allowing more flexibility when testing, and allowing tests to run on models across multiple apps. This would also allow models to work where they have a foreign key to a model in another app. The previous modules list and app label still works as normal so compatibility will not be affected. If a dict of app names to modules is provided, the app_label kw argument is not used.

Motivation and Context

Particularly useful when integrating models from a third party library into your own application.
Issue created a while back: #1521

How Has This Been Tested?

This is something that needs to be discussed as at the moment intializer and finalizer is run as an autouse session fixture, so difficult to override for a single test. Coverage is not an issue as there are no new lines.

Possibilities include:

• Changing initialize_tests fixture to use the new apps/module dict format in which case the older single list format would not be tested.
• Create a completely separate tests directory which ignores the main conftest.py. Probably the main conftest.py would have to be moved into the current tests directory. The new tests directory would have it's own conftest.py using the new style initializer argument format

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added the changelog accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codspeed-hq]

CodSpeed Performance Report

Merging #1895 will not alter performance

_{Comparing primal100:develop (9c83354) with develop (40b427d)}

Summary

✅ 16 untouched benchmarks

[primal100]

Some checks are failing due to

UP007 Use `X | Y` for type annotations

However, this newer way of writing Union types was introduced in Python 3.10 and tortoise-orm still allows support for 3.9, so that's why I still used typing.Union.

[waketzheng]

Some checks are failing due to

UP007 Use `X | Y` for type annotations

However, this newer way of writing Union types was introduced in Python 3.10 and tortoise-orm still allows support for 3.9, so that's why I still used typing.Union.

With this line from __future__ import annotations at the beginning of the file, you are able to use X | Y for Python3.9