Add a function to trigger import of models programatically

[fabienheureux]

import_models

I have a use case where I need to import every models in an async job, and as far as I can see, the import is done in management command and in the views, but there is no dedicated function to achieve this.

Typo

Also, this fixes a typo found in the utils.py file

Github actions / tests

I noticed tests were failing, I fixed them and added github actions in order to run tests for every push / PR in order to detect regression more easily
See an example here: https://github.com/fabienheureux/wagtail-airtable/runs/2247619087?check_suite_focus=true

To be improved: poetry dependencies are not cached yet, I tried an existing implementation of mine that does not work anymore with Github actions (for example https://github.com/Casyfill/pyCombo/blob/master/.github/workflows/release.yml)

[fabienheureux]

I think this is ready to review @KalobTaulien I don't know if this function is worth adding to the documentation ?