Initial affiliate codes implementation (#4382)

* Initial affiliate codes implementation

* some more docs to codes

* sqlx prepare

* Address PR comments

* Address more PR comments

* fix clippy

* Switch to using Json<T> for type-safe responses

apps/labrinth/.sqlx/query-d51d96a9771ce1c3a2987e0790ef25bc55122c934c73418a97ee9cd81f56b251.json

@@ -0,0 +1,17 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "INSERT INTO affiliate_codes (id, created_at, created_by, affiliate)\n            VALUES ($1, $2, $3, $4)",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Int8",
+        "Timestamptz",
+        "Int8",
+        "Int8"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "d51d96a9771ce1c3a2987e0790ef25bc55122c934c73418a97ee9cd81f56b251"
+}