Improve endpoint mediatype regex

Author: C0nquistadore

src/Dibix.Sdk.CodeGeneration/Schema/dibix.endpoints.schema.json

@@ -66,7 +66,7 @@
     },
     "MediaType": {
       "type": "string",
-      "pattern": "^\\w+\\/[-+.\\w*]+$"
+      "pattern": "^([a-z]+|\\*)\\/([-+.a-z\\d]+|\\*)(; charset=[a-z\\d-]+)?$"
     },
     "Body": {
       "type": "object",