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

proto/zitadel/admin.proto

@@ -506,6 +506,40 @@ service AdminService {
         };
     }
 
+    rpc TestSMTPConfigById(TestSMTPConfigByIdRequest) returns (TestSMTPConfigByIdResponse) {
+        option (google.api.http) = {
+            post: "/smtp/{id}/_test";
+            body: "*"
+        };
+
+        option (zitadel.v1.auth_option) = {
+            permission: "iam.write";
+        };
+
+        option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_operation) = {
+            tags: "SMTP Provider";
+            summary: "Test SMTP Provider ";
+            description: "Test an SMTP provider identified by its ID. After testing the provider, the users will receive information about the test results."
+        };
+    }
+
+    rpc TestSMTPConfig(TestSMTPConfigRequest) returns (TestSMTPConfigResponse) {
+        option (google.api.http) = {
+            post: "/smtp/_test";
+            body: "*"
+        };
+
+        option (zitadel.v1.auth_option) = {
+            permission: "iam.write";
+        };
+
+        option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_operation) = {
+            tags: "SMTP Provider";
+            summary: "Test SMTP Provider";
+            description: "Test an SMTP provider. After testing the provider, the users will receive information about the test results."
+        };
+    }
+
     rpc ListSMTPConfigs(ListSMTPConfigsRequest) returns (ListSMTPConfigsResponse) {
         option (google.api.http) = {
             post: "/smtp/_search"
@@ -4257,6 +4291,82 @@ message RemoveSMTPConfigResponse {
     zitadel.v1.ObjectDetails details = 1;
 }
 
+message TestSMTPConfigByIdRequest {
+    string id = 1 [(validate.rules).string = {min_len: 1, max_len: 100}];
+    string receiver_address = 2 [
+        (validate.rules).string = {min_len: 1, max_len: 200, email: true},
+        (google.api.field_behavior) = REQUIRED,
+        (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_field) = {
+            example: "\"noreply@m.zitadel.cloud\"";
+            min_length: 1;
+            max_length: 200;
+        }
+    ];
+}
+
+// This is an empty response
+message TestSMTPConfigByIdResponse {}
+
+message TestSMTPConfigRequest {
+    string sender_address = 1 [
+        (validate.rules).string = {min_len: 1, max_len: 200},
+        (google.api.field_behavior) = REQUIRED,
+        (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_field) = {
+            example: "\"noreply@m.zitadel.cloud\"";
+            min_length: 1;
+            max_length: 200;
+        }
+    ];
+    string sender_name = 2 [
+        (validate.rules).string = {min_len: 1, max_len: 200},
+        (google.api.field_behavior) = REQUIRED,
+        (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_field) = {
+            example: "\"ZITADEL\"";
+            min_length: 1;
+            max_length: 200;
+        }
+    ];
+    bool tls = 3;
+    string host = 4 [
+        (validate.rules).string = {min_len: 1, max_len: 500},
+        (google.api.field_behavior) = REQUIRED,
+        (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_field) = {
+            example: "\"smtp.postmarkapp.com:587\"";
+            description: "Make sure to include the port.";
+            min_length: 1;
+            max_length: 500;
+        }
+    ];
+    string user = 5 [
+        (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_field) = {
+            example: "\"197f0117-529e-443d-bf6c-0292dd9a02b7\"";
+        }
+    ];
+    string password = 6 [
+        (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_field) = {
+            example: "\"this-is-my-password\"";
+        }
+    ];
+    string receiver_address = 7 [
+        (validate.rules).string = {min_len: 1, max_len: 200, email: true},
+        (google.api.field_behavior) = REQUIRED,
+        (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_field) = {
+            example: "\"noreply@m.zitadel.cloud\"";
+            min_length: 1;
+            max_length: 200;
+        }
+    ];
+    string id = 8 [
+        (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_field) = {
+            description: "Zitadel SMTP provider id in case you are not sending the password and want to reuse the stored password";
+            example: "\"267191369515139464\"";
+        }
+    ];
+}
+
+// This is an empty response
+message TestSMTPConfigResponse {}
+
 message ListSMSProvidersRequest {
     //list limitations and ordering
     zitadel.v1.ListQuery query = 1;