types: allow no models argument for automigrate

Fix type definitions to allow zero-argument invocation of
the following database migration methods:
  - `DataSource.automigrate()`
  - `DataSource.autoupdate()`

Implementation-wise, when no model names are specified, then ALL models
attached to the datasource are migrated.

Signed-off-by: Miroslav Bajtoš <mbajtoss@gmail.com>

types/datasource.d.ts

@@ -140,13 +140,13 @@ export declare class DataSource extends EventEmitter {
    */
   attach(modelClass: ModelBaseClass): ModelBaseClass;
 
-  automigrate(models: string | string[]): Promise<void>;
+  automigrate(models?: string | string[]): Promise<void>;
   // legacy callback style
-  automigrate(models: string | string[], callback: Callback): void;
+  automigrate(models: string | string[] | undefined, callback: Callback): void;
 
-  autoupdate(models: string | string[]): Promise<void>;
+  autoupdate(models?: string | string[]): Promise<void>;
   // legacy callback style
-  autoupdate(models: string | string[], callback: Callback): void;
+  autoupdate(models: string | string[] | undefined, callback: Callback): void;
 
   discoverModelDefinitions(
     options?: Options,