✨(backend) add mimetype detection logic from drive

Reused the logic developed by the team working on drive.
This is usefull for our own upload file backend (that will
come in later commits).

Dockefile was updated to add a required system dependency.

We might want to put this shared logic in a lib.

Dockerfile

@@ -39,6 +39,7 @@ ARG MEET_STATIC_ROOT=/data/static
 
 RUN apk add \
   pango \
+  libmagic \
   rdfind
 
 # Copy installed python dependencies
@@ -68,6 +69,7 @@ RUN apk --no-cache add \
   gettext \
   libffi-dev \
   pango \
+  libmagic \
   shared-mime-info