🚚(backend) rename Impress to Meet

I have updated all references of "Impress" to "Meet".
Migrations were manually updated and not regenerated. Never-mind,
they all will be squashed before the first release.

I have also searched for reference to "Magnify", and replaced them
by "Meet".

While updating the backend sources, I have also fixed other parts of
the project, namely:
- Compose file
- Github documentation and CI
- Makefile commands

src/backend/core/apps.py

@@ -1,11 +1,11 @@
-"""Impress Core application"""
+"""Meet Core application"""
 # from django.apps import AppConfig
 # from django.utils.translation import gettext_lazy as _
 
 
 # class CoreConfig(AppConfig):
-#     """Configuration class for the impress core app."""
+#     """Configuration class for the Meet core app."""
 
 #     name = "core"
 #     app_label = "core"
-#     verbose_name = _("impress core application")
+#     verbose_name = _("meet core application")