Enable Email as a MFA method/option (#68)

This adds Email as a multi-factor authentication method/option. It reuses the `VerificationCode` for the code generation and validation.

It also refactors the email templating for easier repurposing.

Finally, it has a small Deno version bump.

Closes #25

docker-compose.yml

@@ -1,6 +1,6 @@
 services:
   website:
-    image: ghcr.io/bewcloud/bewcloud:v2.0.0
+    image: ghcr.io/bewcloud/bewcloud:v2.1.0
     restart: always
     ports:
       - 127.0.0.1:8000:8000