feat: add available providers list

ApiDto/Common/OAuthProvider.cs

@@ -0,0 +1,22 @@
+namespace Mirea.Api.Dto.Common;
+
+/// <summary>
+/// Represents different OAuth providers for authentication.
+/// </summary>
+public enum OAuthProvider
+{
+    /// <summary>
+    /// OAuth provider for Google.
+    /// </summary>
+    Google,
+
+    /// <summary>
+    /// OAuth provider for Yandex.
+    /// </summary>
+    Yandex,
+
+    /// <summary>
+    /// OAuth provider for Mail.ru.
+    /// </summary>
+    MailRu
+}