🧑‍💻(views) render email's template

THis feature is inspired by Joanie. Add two new urls to render Emails
HTML and Text templates.

Developpers can render the email template they are working on. When necessary,
run make mails-build, and reload `_debug__/mail/hello_html`, it will re-render
the updated email template.

Also, I have copy/pasted one template extra tags from Joanie, which loads
bas64 string from static images. This code is necessary to render the dummy
template `hello.html`.

src/backend/debug/urls.py

@@ -0,0 +1,21 @@
+"""Debug Urls to check the layout of emails"""
+
+from django.urls import path
+
+from .views import (
+    DebugViewHtml,
+    DebugViewTxt,
+)
+
+urlpatterns = [
+    path(
+        "__debug__/mail/hello_html",
+        DebugViewHtml.as_view(),
+        name="debug.mail.hello_html",
+    ),
+    path(
+        "__debug__/mail/hello_txt",
+        DebugViewTxt.as_view(),
+        name="debug.mail.hello_txt",
+    ),
+]

src/backend/debug/views.py

@@ -0,0 +1,29 @@
+"""Debug Views to check the layout of emails"""
+
+from django.views.generic.base import TemplateView
+
+
+class DebugBaseView(TemplateView):
+    """Debug View to check the layout of emails"""
+
+    def get_context_data(self, **kwargs):
+        """Generates sample datas to have a valid debug email"""
+
+        context = super().get_context_data(**kwargs)
+        context["title"] = "Development email preview"
+        context["email"] = "random@gmail.com"
+        context["fullname"] = "robert"
+
+        return context
+
+
+class DebugViewHtml(DebugBaseView):
+    """Debug View for HTML Email Layout"""
+
+    template_name = "mail/html/hello.html"
+
+
+class DebugViewTxt(DebugBaseView):
+    """Debug View for Text Email Layout"""
+
+    template_name = "mail/text/hello.txt"