✨(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- Helm sources are outdated.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/mail/mjml/partial/footer.mjml

@@ -0,0 +1,9 @@
+<mj-section padding="0">
+  <mj-column>
+    <mj-text mj-class="text--small" align="center" padding="20px 20px">
+      {% blocktranslate with href=site.url name=site.name trimmed %}
+        This mail has been sent to {{email}} by <a href="{{href}}">{{name}}</a>
+      {% endblocktranslate %}
+    </mj-text>
+  </mj-column>
+</mj-section>

src/mail/mjml/partial/header.mjml

@@ -0,0 +1,46 @@
+<mj-head>
+    <mj-title>{{ title }}</mj-title>
+    <mj-preview>
+        <!--
+            We load django tags here, in this way there are put within the body in html output
+            so the html-to-text command includes it within its output
+        -->
+        {% load i18n static extra_tags %}
+        {{ title }}
+    </mj-preview>
+    <mj-attributes>
+        <mj-font name="Roboto" href="https://fonts.googleapis.com/css2?family=Roboto:wght@400;700;900&display=swap" />
+        <mj-all
+                font-family="Roboto, -apple-system, BlinkMacSystemFont, 'Segoe UI', Oxygen, Ubuntu, Cantarell, 'Helvetica Neue', sans-serif"
+                font-size="16px"
+                line-height="1.5em"
+                color="#3A3A3A"
+        />
+    </mj-attributes>
+    <mj-style>
+        /* Reset */
+        h1, h2, h3, h4, h5, h6, p {
+            margin: 0;
+            padding: 0;
+        }
+
+        a {
+            color: inherit;
+        }
+    </mj-style>
+    <mj-style>
+        /* Global styles */
+        h1 {
+            color: #161616;
+            font-size: 2rem;
+            line-height: 1em;
+            font-weight: 700;
+        }
+
+        .wrapper {
+            background: #FFFFFF;
+            border-radius: 0 0 6px 6px;
+            box-shadow: 0 0 6px rgba(2 117 180 / 0.3);
+        }
+    </mj-style>
+</mj-head>