feat: send test mail (#7968)

# Which Problems Are Solved

- Zitadel doesn't have a way to test SMTP settings either before
creating a new provider or once the SMTP provider has been created.
- Zitadel SMTP messages can be more informative for usual errors

# How the Problems Are Solved

- A new step is added to the new/update SMTP provider wizard that allows
us to test a configuration. The result is shown in a text area.
- From the table of SMTP providers you can test your settings too.
- The email address to send the email is by default the email address
for the logged in user as suggested.
- Some of the SMTP error messages have been changed to give more
information about the possible situation. For example: could not contact
with the SMTP server, check the port, firewall issues... instead of
could not dial

Here's a video showing this new option in action:


https://github.com/zitadel/zitadel/assets/30386061/50128ba1-c9fa-4481-8eec-e79a3ca69bda

# Additional Changes

Replace this example text with a concise list of additional changes that
this PR introduces, that are not directly solving the initial problem
but are related.
For example:
- The docs explicitly describe that the property XY is mandatory
- Adds missing translations for validations.

# Additional Context

- Closes #4504

internal/api/grpc/admin/smtp.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/zitadel/zitadel/internal/api/authz"
 	"github.com/zitadel/zitadel/internal/api/grpc/object"
+	"github.com/zitadel/zitadel/internal/notification/channels/smtp"
 	admin_pb "github.com/zitadel/zitadel/pkg/grpc/admin"
 )
 
@@ -128,3 +129,29 @@ func (s *Server) DeactivateSMTPConfig(ctx context.Context, req *admin_pb.Deactiv
 		Details: object.DomainToAddDetailsPb(result),
 	}, nil
 }
+
+func (s *Server) TestSMTPConfigById(ctx context.Context, req *admin_pb.TestSMTPConfigByIdRequest) (*admin_pb.TestSMTPConfigByIdResponse, error) {
+	err := s.command.TestSMTPConfigById(ctx, authz.GetInstance(ctx).InstanceID(), req.Id, req.ReceiverAddress)
+	if err != nil {
+		return nil, err
+	}
+
+	return &admin_pb.TestSMTPConfigByIdResponse{}, nil
+}
+
+func (s *Server) TestSMTPConfig(ctx context.Context, req *admin_pb.TestSMTPConfigRequest) (*admin_pb.TestSMTPConfigResponse, error) {
+	config := smtp.Config{}
+	config.Tls = req.Tls
+	config.From = req.SenderAddress
+	config.FromName = req.SenderName
+	config.SMTP.Host = req.Host
+	config.SMTP.User = req.User
+	config.SMTP.Password = req.Password
+
+	err := s.command.TestSMTPConfig(ctx, authz.GetInstance(ctx).InstanceID(), req.Id, req.ReceiverAddress, &config)
+	if err != nil {
+		return nil, err
+	}
+
+	return &admin_pb.TestSMTPConfigResponse{}, nil
+}