✨(project) Django boilerplate

This commit introduces a boilerplate inspired by https://github.com/numerique-gouv/impress.
The code has been cleaned to remove unnecessary Impress logic and dependencies.

Changes made:
- Removed Minio, WebRTC, and create bucket from the stack.
- Removed the Next.js frontend (it will be replaced by Vite).
- Cleaned up impress-specific backend logics.

The whole stack remains functional:
- All tests pass.
- Linter checks pass.
- Agent Connexion sources are already set-up.

Why clear out the code?

To adhere to the KISS principle, we aim to maintain a minimalist codebase. Cloning Impress
allowed us to quickly inherit its code quality tools and deployment configurations for staging,
pre-production, and production environments.

What’s broken?
- The tsclient is not functional anymore.
- Some make commands need to be fixed.
- Helm sources are outdated.
- Naming across the project sources are inconsistent (impress, visio, etc.)
- CI is not configured properly.

This list might be incomplete. Let's grind it.

src/backend/demo/data/template/css.txt

@@ -0,0 +1,18 @@
+body {
+  background: white; 
+  font-family: arial
+}
+.header {
+  display: flex;
+  justify-content: space-between;
+}
+.header img {
+  width: 5cm;
+  margin-left: -0.4cm;
+}
+.body{
+  margin-top: 1.5rem
+}
+img {
+  max-width: 100%;
+}