[FIX] letsencrypt. Use char instead of text fields for config.

res.config.settings does not allow Text fields for config_parameter fields. The solution to overcome this is generating
warnings in runbot. As varchar fields without size are to all intents and purposes the same as text fields in postgress,
and can be painlessly and automatically converted, the field type is changed.

letsencrypt/models/res_config_settings.py

@@ -12,13 +12,13 @@ DNS_SCRIPT_DEFAULT = """# Write your script here
 class ResConfigSettings(models.TransientModel):
     _inherit = "res.config.settings"
 
-    letsencrypt_altnames = fields.Text(
+    letsencrypt_altnames = fields.Char(
         string="Domain names",
         default="",
         help=(
             "Domains to use for the certificate. " "Separate with commas or newlines."
         ),
-        force_config_parameter="letsencrypt.altnames",
+        config_parameter="letsencrypt.altnames",
     )
     letsencrypt_dns_provider = fields.Selection(
         selection=[("shell", "Shell script")],
@@ -31,7 +31,7 @@ class ResConfigSettings(models.TransientModel):
         ),
         config_parameter="letsencrypt.dns_provider",
     )
-    letsencrypt_dns_shell_script = fields.Text(
+    letsencrypt_dns_shell_script = fields.Char(
         string="DNS update script",
         help=(
             "Write a shell script that will update your DNS TXT records. "
@@ -39,13 +39,13 @@ class ResConfigSettings(models.TransientModel):
             "$LETSENCRYPT_DNS_DOMAIN variables."
         ),
         default=DNS_SCRIPT_DEFAULT,
-        force_config_parameter="letsencrypt.dns_shell_script",
+        config_parameter="letsencrypt.dns_shell_script",
     )
     letsencrypt_needs_dns_provider = fields.Boolean()
-    letsencrypt_reload_command = fields.Text(
+    letsencrypt_reload_command = fields.Char(
         string="Server reload command",
         help="Fill this with the command to restart your web server.",
-        force_config_parameter="letsencrypt.reload_command",
+        config_parameter="letsencrypt.reload_command",
     )
     letsencrypt_testing_mode = fields.Boolean(
         string="Use testing server",
@@ -90,25 +90,3 @@ class ResConfigSettings(models.TransientModel):
                 raise exceptions.ValidationError(
                     _("You didn't write a DNS update script!")
                 )
-
-    @api.model
-    def _get_classified_fields(self):
-        """config_parameter is inexplicably allowed on Char but not Text.
-
-        ir.config_parameter values can handle newlines, even in the web
-        interface, so there doesn't seem to be a good reason for this.
-
-        Add "force_config_parameter" as an alternative that ignores types.
-        """
-        # Note: As of writing, Odoo 13 has this limit and Odoo 14 isn't out
-        # Whenever migrating, make sure this is still necessary
-        classified = super()._get_classified_fields()
-        new_other = []
-        for name in classified["other"]:
-            field = self._fields[name]
-            if hasattr(field, "force_config_parameter"):
-                classified["config"].append((name, field.force_config_parameter))
-            else:
-                new_other.append(name)
-        classified["other"] = new_other
-        return classified