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/static/i18n/en.yaml

@@ -53,11 +53,24 @@ Errors:
     NotFound: SMS configuration not found
     AlreadyActive: SMS configuration already active
     AlreadyDeactivated: SMS configuration already deactivated
+  SMTP:
+    NotEmailMessage: message is not EmailMessage
+    RequiredAttributes: subject, recipients and content must be set but some or all of them are empty
+    CouldNotSplit: could not split host and port for connect to smtp
+    CouldNotDial: could not contact with the SMTP server, check the port, firewall issues...
+    CouldNotDialTLS: could not contact with the SMTP server using TLS, check the port, firewall issues...
+    CouldNotCreateClient: could not create smtp client
+    CouldNotStartTLS: could not start tls
+    CouldNotAuth: could not add smtp auth, check if both your user and password are correct, if they're correct maybe your provider requires an auth method not supported by ZITADEL
+    CouldNotSetSender: could not set sender
+    CouldNotSetRecipient: could not set recipient
   SMTPConfig:
+    TestPassword: Password for test not found
     NotFound: SMTP configuration not found
     AlreadyExists: SMTP configuration already exists
     AlreadyDeactivated: SMTP configuration already deactivated
     SenderAdressNotCustomDomain: The sender address must be configured as custom domain on the instance.
+    TestEmailNotFound: Email address for test not found
   Notification:
     NoDomain: No Domain found for message
   User: