feat: http provider signing key addition (#10641)

# Which Problems Are Solved

HTTP Request to HTTP providers for Email or SMS are not signed.

# How the Problems Are Solved

Add a Signing Key to the HTTP Provider resources, which is then used to
generate a header to sign the payload.

# Additional Changes

Additional tests for query side of the SMTP provider.

# Additional Context

Closes #10067

---------

Co-authored-by: Marco A. <marco@zitadel.com>
(cherry picked from commit 8909b9a2a6)

internal/api/grpc/admin/email.go

@@ -55,8 +55,9 @@ func (s *Server) AddEmailProviderHTTP(ctx context.Context, req *admin_pb.AddEmai
 		return nil, err
 	}
 	return &admin_pb.AddEmailProviderHTTPResponse{
-		Details: object.DomainToChangeDetailsPb(config.Details),
-		Id:      config.ID,
+		Details:    object.DomainToChangeDetailsPb(config.Details),
+		Id:         config.ID,
+		SigningKey: config.SigningKey,
 	}, nil
 }
 
@@ -66,7 +67,8 @@ func (s *Server) UpdateEmailProviderHTTP(ctx context.Context, req *admin_pb.Upda
 		return nil, err
 	}
 	return &admin_pb.UpdateEmailProviderHTTPResponse{
-		Details: object.DomainToChangeDetailsPb(config.Details),
+		Details:    object.DomainToChangeDetailsPb(config.Details),
+		SigningKey: config.SigningKey,
 	}, nil
 }