🔧(backend) fix Pylint configurations

Removing the __init__.py makes it impossible for Pylint to get the sources
to lint from the root folder. We manually set all the paths pylint will lint.

That's not a big deal, as we'll remove Pylint any soon to rely only on ruff.
I took inspiration from marsha or magnify project.

I removed the now useless bash script to run Pylint command. It saves us
wrapper! Plus, having a lint command running with different option locally
and in the CI was quite a pain.

Locally linter was running on diff files; Fixed! CI and make command has now
the same behavior.

Makefile

@@ -141,7 +141,7 @@ lint-ruff-check: ## lint back-end python sources with ruff
 
 lint-pylint: ## lint back-end python sources with pylint only on changed files from main
 	@echo 'lint:pylint started…'
-	bin/pylint --diff-only=origin/main
+	@$(COMPOSE_RUN_APP) pylint meet demo core
 .PHONY: lint-pylint
 
 test: ## run project tests