feat(mobile) Add OAuth Login On Mobile (#990)

* Added return type for oauth/callback

* Remove console.log

* Redirect app

* Wording

* Added loading state change

* Added OAuth login on mobile

* Return correct status for  correct redirection

* Auto discovery OAuth Login

mobile/lib/modules/login/services/oauth.service.dart

@@ -0,0 +1,39 @@
+import 'package:immich_mobile/shared/services/api.service.dart';
+import 'package:openapi/api.dart';
+import 'package:flutter_web_auth/flutter_web_auth.dart';
+
+// Redirect URL = app.immich://
+
+class OAuthService {
+  final ApiService _apiService;
+  final callbackUrlScheme = 'app.immich';
+
+  OAuthService(this._apiService);
+
+  Future<OAuthConfigResponseDto?> getOAuthServerConfig(
+    String serverEndpoint,
+  ) async {
+    _apiService.setEndpoint(serverEndpoint);
+
+    return await _apiService.oAuthApi.generateConfig(
+      OAuthConfigDto(redirectUri: '$callbackUrlScheme:/'),
+    );
+  }
+
+  Future<LoginResponseDto?> oAuthLogin(String oauthUrl) async {
+    try {
+      var result = await FlutterWebAuth.authenticate(
+        url: oauthUrl,
+        callbackUrlScheme: callbackUrlScheme,
+      );
+
+      return await _apiService.oAuthApi.callback(
+        OAuthCallbackDto(
+          url: result,
+        ),
+      );
+    } catch (e) {
+      return null;
+    }
+  }
+}