[PM-22678] Send email otp authentication method (#6255)

feat(auth): email OTP validation, and generalize authentication interface

- Generalized send authentication method interface
- Made validate method async
- Added email mail support for Handlebars
- Modified email templates to match future implementation

fix(auth): update constants, naming conventions, and error handling

- Renamed constants for clarity
- Updated claims naming convention
- Fixed error message generation
- Added customResponse for Rust consumption

test(auth): add and fix tests for validators and email

- Added tests for SendEmailOtpRequestValidator
- Updated tests for SendAccessGrantValidator

chore: apply dotnet formatting

src/Core/Models/Mail/Auth/DefaultEmailOtpViewModel.cs

@@ -0,0 +1,12 @@
+namespace Bit.Core.Models.Mail.Auth;
+
+/// <summary>
+/// Send email OTP view model
+/// </summary>
+public class DefaultEmailOtpViewModel : BaseMailModel
+{
+    public string? Token { get; set; }
+    public string? TheDate { get; set; }
+    public string? TheTime { get; set; }
+    public string? TimeZone { get; set; }
+}