Define knwon plugins

Author: Shinigami92

src/index.d.ts

@@ -2,6 +2,7 @@ import type { Environments } from './env';
 import type { Extends } from './extends';
 import type { Overrides } from './overrides';
 import type { Parser, ParserOptions } from './parser-options';
+import type { Plugin } from './plugin';
 import type { Rules } from './rules';
 import type { Settings } from './settings';
 
@@ -52,7 +53,7 @@ export interface EslintConfig {
    *
    * @see [Configuring Plugins](https://eslint.org/docs/user-guide/configuring/plugins#configuring-plugins)
    */
-  plugins?: string[];
+  plugins?: Plugin[];
   /**
    * Rules.
    *

src/plugin.d.ts

@@ -0,0 +1,4 @@
+import type { LiteralUnion } from './utility-types';
+
+/** Plugin. */
+export type Plugin = LiteralUnion<'@typescript-eslint' | 'prettier' | 'import' | 'jsdoc' | 'spellcheck'>;