Added Discord to default upstream oauth2 providers, regenerated config schema

Author: ChurchOfTheSubgenius

crates/config/src/sections/upstream_oauth2.rs

@@ -432,6 +432,7 @@ pub struct Provider {
     ///  - `github`
     ///  - `gitlab`
     ///  - `twitter`
+    ///  - `discord`
     #[serde(skip_serializing_if = "Option::is_none")]
     pub brand_name: Option<String>,
 

docs/config.schema.json

@@ -1945,7 +1945,7 @@
           "type": "string"
         },
         "brand_name": {
-          "description": "A brand identifier used to customise the UI, e.g. `apple`, `google`, `github`, etc.\n\nValues supported by the default template are:\n\n- `apple` - `google` - `facebook` - `github` - `gitlab` - `twitter`",
+          "description": "A brand identifier used to customise the UI, e.g. `apple`, `google`, `github`, etc.\n\nValues supported by the default template are:\n\n- `apple` - `google` - `facebook` - `github` - `gitlab` - `twitter` - `discord`",
           "type": "string"
         },
         "client_id": {