fix: add OAuth2Adapter interface for authentication

Author: SerVitasik

adminforth/types/Adapters.ts

@@ -24,3 +24,9 @@ export interface CompletionAdapter {
     error?: string;
   }>;
 }
+
+export interface OAuth2Adapter {
+  getAuthUrl(): string;
+  getTokenFromCode(code: string, redirect_uri: string): Promise<{ email: string }>;
+  getIcon(): string;
+}