Revert generate removing

modoboa_installer/config_dict_template.py

@@ -30,6 +30,10 @@ ConfigDictTemplate = [
     {
         "name": "certificate",
         "values": [
+            {
+                "option": "generate",
+                "default": "true",
+            },
             {
                 "option": "type",
                 "default": "self-signed",

modoboa_installer/ssl.py

@@ -148,6 +148,10 @@ class LetsEncryptCertificate(CertificateBackend):
 def get_backend(config):
     """Return the appropriate backend."""
     cert_type = config.get("certificate", "type")
+    condition = (not config.getboolean("certificate", "generate") and
+                 cert_type != "manual")
+    if condition:
+        return None
     if cert_type == "letsencrypt":
         return LetsEncryptCertificate(config)
     if cert_type == "manual":