feat: Add option keepUnknownIndexes to retain indexes which are not specified in schema (#9857)

src/Options/index.js

@@ -25,6 +25,9 @@ export interface SchemaOptions {
   /* Is true if Parse Server will reject any attempts to modify the schema while the server is running.
   :DEFAULT: false */
   lockSchemas: ?boolean;
+  /* (Optional) Keep indexes that are present in the database but not defined in the schema. Set this to `true` if you are adding indexes manually, so that they won't be removed when running schema migration. Default is `false`.
+  :DEFAULT: false */
+  keepUnknownIndexes: ?boolean;
   /* Execute a callback before running schema migrations. */
   beforeMigration: ?() => void | Promise<void>;
   /* Execute a callback after running schema migrations. */