Plaster-yaml

* Remove python 3.8 support
* Substitute environment variable with [envsub](https://pypi.org/project/envsub/)
* Add typing support
* CI and packaging update

* Fix the loader setup_logging interface method. defaults is not a mandatory parameter.

* Rename plaster_yaml to plaster-yaml

* /!\BREAKING CHANGE Restore the autoregistrion of the plaster-yaml file format in plaster.

You don't need to register the plaster-yaml entrypoint for file format .yaml, .yml and .json

Remove the entrypoint registered in your package for the migration

Fix for poetry, application that use plater-yaml registered the plugin with
those lines, remove them to avoid the conflict.


[tool.poetry.plugins."plaster.loader_factory"]
"file+yaml" = "plaster_yaml:Loader"

* Revert register the plaster yaml entrypoints directly, fixing a breaking change

* Also fix non namespace packaging container underscores